I'm a novice builder, but for what it's worth here's what I'd do:

1. Fit your screws and make an assessment based on the the hardware being fastened down correctly.
2. If it's still bad (and it may prove to be just fine...) then get a quote from someone local to you about getting 'em straightened. The screws probably won't seem like such a bargain by that point, but hey - chalk it up to experience. It'll be less hassle than sending back/waiting on new screws etc.
3. If it's burning you up and you feel strongly that you've got the raw end of the deal* - then write him a calm email explaining your issue.

*Chai is not in the business of selling rubbish - he gets plenty of recommendations and repeat business for a reason, sometimes things don't work out but I'm sure he'll try to help you as best he can.

4. Fit your screws and make an assessment based on the the hardware being fastened down correctly.

Wal.