If your frame bent, then it's good you found out now before installing the engine.
If you want, you can check out Goodwill for a cheap used bike. Some people leave really nice bikes that would be perfectly good for an motorized bicycle kit. I remember when I was considering buying a kit, I was at Goodwill and saw this awesome classic bike that had fenders, a big headlight, sleek frame, army green paint, and everything. The next day I went to Goodwill to get it and it was gone.
Fortunately I still had the old mountain bike that I was going to use all along so that's the bike I've been running now. Still, that bike from Goodwill would have been sick!