If it wasn't bowed before you taped it, I'd consider untaping it and trying again. I've pulled tape off the wing before, and it pulls some of the paint off. I used a red acrylic paint to touch up the white spots. The elevator is a tad thinner.

If you're worried about damaging the foam, you can cut the tape and try again. Maybe the best solution.

I don't really recommend heating it up. I did this to my last SS fin to straighten it up after it had bowed and it didn't really work out as well as I had hoped. The tape will likely shrink a bit too, or stretch, if you heat and pull, but at a different rate than the foam...