I was accepted into a good school for my field and met with a professor I really liked at open house. I later had a phone conversation with him a few weeks after open house and he said I could join his group and start working this summer. The next day I received NSF and he emailed me listing reasons I should join his group. I emailed him back saying I would make my final decision the following week.
However, I have emailed him twice saying I won NSF and would like to join his group, but he has yet to respond. Should I go ahead and accept the school's offer? I'm worried the offer to join his group has been taken back.