By all means, bring this up. Something like that goes a long way:
Hey manager, I think this part of code is sketchy. At first glance it can introduce a bug. I am not sure how it passed tests, so can we double-check? When do you have time to sit down and discuss it?
By coming forward early you display professionalism. That should be your manager's decision what to do with this information, and their responsibility. Maybe they'll decide that is not a bug, or that can be fixed later, or decide to push patch immediately.
I think that worse case scenario is that there is a bug, and customer will discover it eventually. People will spend time looking for issue, and very well might find that it is in your part of code. Bug happen, no big deal, but you'll have to fix it.