[partisan]

I think you are OK to cancel at this point without fear of retribution. The tech industry is fairly large. You won't find doors locked to you. In fact, you did so well that your previous employer thought of you for another internship. That's a huge win.

The minimum requirement is that you reneg as early as possible, do so politely and professionally, and finally, don't think about it thereafter. Your career is ahead of you.