I just found out I have an uti. I have augmentation surgery tomorrow, will this interfere with my surgery?

It won't necessarily interfere with your surgery, but because this surgery is elective, my personal recommendation would be to postpone your surgery until you have recovered. 

Yes I would cancel your surgery and I would not  want to be in a position where we place implant  and could potentially become infected in someone with an active infection.  It is important to make sure you are off all medications that can make you bleed and make sure that there is no active infection or any boils or pimples in the area of operation because we want to make sure that we perform the operation with the very lowest risk possible and did not risk an infection.

A basic concept is never to undergo elective surgery if you have an active infection. This is particularly true when dealing with breast augmentation in that you do not want to risk infecting the implants. The best advice would be to postpone your surgery until your uti is treated and you have a negative urine culture and urinalysis.