I also would go to the assessment. It could be that you do meet the criteria for PTSD, even if you don't think you have it. Or that they would treat you anyway. If you go to the first appointment, and they don't think you should be working with them (or if you think that), then it's not like you'd be delaying anyone being seen by much, maybe a day. And maybe it would help you to get an appointment with someone else, like they could give you a referral. Or maybe they'll be able to help you.