The 20-year-old would have been part of Paul Simpson's squad in South Korea, but opted to remain in Glasgow.
"I made a decision and I'm proud of that decision," Roberts said.
"I've got a massive final to play. There's an incentive for all of us to go all the way."
Celtic can seal the treble - for only the third time in the club's history - if they overcome Aberdeen on Saturday at Hampden.
It may be Roberts' last game for the club, since he is due to return to parent side Manchester City in the summer, after 18 months at Celtic Park.
"To win the treble at this massive club would be big for me and hopefully we can do that," Roberts said.
"It's a massive trophy to be a part of and a big one in Scottish football. So it's important for all the players, not just me, to go into it 100% and we'll do that.
"We [have] the same focus, the same mindset and go into the final in the same way [as every other game this season]."
Celtic have defeated Aberdeen in all five of their meetings this season, but Roberts insists the Pittodrie side will be a "tough test" because "they have a point to prove".
Roberts has been in impressive form in recent weeks - scoring six goals in his last 10 games - and credits the influence of manager Brendan Rodgers for the level of his performances.
"I'm feeling good at the moment, confident, and as a player you need to feel good about yourself, to go into a game feeling positive and do what you do best," Roberts said.
"As a player, you're striving for games and form, and you become a better player for that. The time I've been here I've come on leaps and bounds, thanks to the players and the staff here. It's been a good year and it's not over yet.
"[Rodgers] is a top coach, and he's brought all the players onto a different level. This year we've been unplayable at times and that's been down to his management, his coaching has been brilliant.
"He loves working with young players, he's done that with me, Moussa [Dembele] and Kieran [Tierney] and we've gone up a gear this season, which is important for our careers as well as Celtic."
Roberts also expressed his condolences for the families affected by the Manchester bombing.
"It's a tragic thing to happen in any part of the world, but especially somewhere so close," he said.
"To go to a concert and for a bomb to go off, it's not good and our thoughts are with all the families end everyone in Manchester. It's good that we unite and get behind the country."
Celtic's on-loan attacker Patrick Roberts has no regrets over choosing to stay with Celtic for the Scottish Cup final rather than playing for England at the Under-20 World Cup.