Could I submit a paper that I'm not sure about its proof?
It is your responsibility, not the referees', to make sure that a published proof is correct.

The reviewers should make sure that the results have some merit; some check proofs line-by-line, and some merely check that the result is plausible and that the proof methodology looks sound. Sometimes errors slip by. Nevertheless, if the result later turns out wrong, your reputation is at stake, not the one of the reviewers.

So speak with your advisor and make sure that your proof is correct before you submit. It might be the case that the proof is correct and you just haven't grasped all the details because you have less experience. Or it might be the case that there is a flaw to address and correct, in which case you should act before submission.

It is not a good research mentality to think "We only have to fool convince one or two referees", in my opinion.