Kezia Dugdale was speaking after Unite boss Len McCluskey said he "can't see" Labour winning on 8 June.
Mr McCluskey later distanced himself from the remarks, insisting that he was "now full of optimism" about the party's chances.
Referring to Mr McCluskey's original comments, Ms Dugdale said: "I think he is wrong. I hope he's wrong."
In an interview with Politico, Mr McCluskey suggested that winning 200 seats - nearly 30 fewer than in 2015 - would be a "successful" result for Mr Corbyn, and it would be "extraordinary" if the party won the election.
But asked about his comment on Wednesday morning, he said: "I am now full of optimism. If I was having that interview now I would not be making those comments."
Mr McCluskey said he was "now convinced that the polls will change" and that "Labour is in with a real chance", describing the party's campaign as "brilliant".
Asked on the Good Morning Scotland programme about the union leader's original remarks, Ms Dugdale said success for the party would mean "winning".
She said she wanted the "Tories out of office and a Labour government in its place", but would not put a figure on how many seats she was hopeful of winning in Scotland, where the party returned only one MP in 2015.
"I want to make progress in Scotland, I want to win more seats, I want to reduce the majority of SNP MPs in many other seats," she said.
"The reality is that in the vast majority of seats across Scotland's central belt it is the Labour Party that stands a very strong second to the SNP."
Mr Corbyn said in March that he would be "absolutely fine" with Scotland having a second independence referendum if the Scottish Parliament asked for one.
His comment was condemned at the time by senior party figures in Scotland - with justice spokeswoman, Jackie Baillie, describing Mr Corbyn as "misguided and irresponsible" while MP Ian Murray said the leader was "destroying the party".
And Labour's general election manifesto, which was unveiled by Mr Corbyn on Tuesday, says the party will "work tirelessly" to oppose a referendum.
Ms Dugdale insisted the party was not sending out mixed messages on the issue, saying it was "very clear" that everyone in the Labour movement opposed independence and a second referendum on the basis that it would lead to "turbo-charged austerity" and "Â£15bn of cuts".
She said people across Scotland were tired of politics in Scotland being dominated by the constitution.
But she added: "It is a huge issue - people are angry that they might be forced to answer that question again.
"So what I am saying clearly is that with Labour you get a clear promise of opposition to independence and an independence referendum.
"But you also get a lot more than that - this is where the Tories and Ruth Davidson fall short. We have got a transformative plan to transform this country, so you can oppose independence but also vote for investment in our public services."
Good Morning Scotland interviewed SNP leader Nicola Sturgeon on Monday, and is due to speak to Liberal Democrat leader Willie Rennie on Thursday, and Scottish Conservative leader Ruth Davidson on Friday.
In a series of interviews on BBC Radio Scotland's Good Morning Scotland programme, each main party leader made their campaign pitch ahead of the 8 June election.
Nicola Sturgeon - Scottish National Party
Nicola Sturgeon has said a vote for the SNP would strengthen Scotland's hand over Brexit and allow her to argue for a seat at the negotiating table. The Scottish government wants Scotland to remain in the EU - and in particular the single market. Ms Sturgeon told the BBC: "What I am saying in this election is that we have an opportunity, by how we vote, to give those proposals democratic legitimacy. And, by voting for the SNP, to give me the ability to strengthen Scotland's hands in those [Brexit] negotiations, get a seat at the negotiating table and argue for Scotland's place in the single market."
Willie Rennie - Scottish Liberal Democrats
There is no inconsistency in supporting a second referendum on Brexit but not on independence, the Scottish Lib Dem leader Willie Rennie has said. The Liberal Democrat manifesto says UK voters should be offered a vote on the final deal to leave the EU. But the party is firmly opposed to another referendum on whether Scotland should be independent. Mr Rennie told the BBC: "I think the British people, not just Theresa May, not just the MPs, not just the Conservatives, should decide on whether that deal is good enough or not."
Ruth Davidson - Scottish Conservative
Scottish Conservative leader Ruth Davidson said there were issues around why Scotland appeared to be "uniquely unattractive" to immigrants. She told BBC Radio's Good Morning Scotland programme that being the "highest taxed part" of the UK disadvantaged the country. She added: "I have my own theories about this in terms of the fact that we are the highest taxed part of the UK, the fact that we have an economy that is shrinking not growing when the rest of the UK economy is growing."
The leader of Scottish Labour has insisted that she thinks the party can win next month's general election.