I am scheduled tomorrow and 2:30 for breast augmentation and i had halve a can of beer: is that ok?

Ask your doctor, but: For average healthy person, consuming a half can of beer would not affect the safety of anesthesia & surgery. But in confronting yes or no to a concern like the one you presented, let the importance of long-term effect from what you would decide what you should do now. So, I would say your planned surgery is more important than short-term pleasure from beer drinking. Then, you decide.

Probably: It is probably OK, but you should call the office of your surgeon and verify that. I would probably not have anymore, and I would be sure they are aware of the current one. Good luck with your surgery.