Retake it with an "A" and move on. It would be a huge waste of time to retake the same class 3 or 4 times and honestly would not offer much benefit. A 3.5 is a great GPA and is nothing to fret about.
I'm honestly surprised your school would let you take the class again. Usually there is a policy in place that let's you retake a class you got a "D" or "F" in but once you get a "C" or better that's it. I'm sure different schools have different policies on this and some would love you to spend the $$.
Retake it and get an "A" and get some other things to make your application sparkle to the adcoms (experience, PCAT, etc)