Well, my first reaction is to get that teacher out of the picture! If she did actually say no one should be friends with him and did make him run for extended periods of time I would file a formal complaint with the school. Totally inappropriate and NOT someone you want helping guide the direction of your child's education.
Regarding denial - I went through a very serious depression feeling like I was in denial but just couldn't see it. I was scared because so many people were telling me DS was on the spectrum and I just couldn't accept it because it just seemed wrong. If I hadn't taken him to the dev ped, I am pretty sure he would have an ASD diagnosis because its very hard to listen to your gut when many "experts" are telling you different. I don't have an answer for you, but I do think you should be willing to question your own position pretty closely. If you examine it and STILL feel like there is something not right, then I would keep looking for answers.
I know many people feel that a diagnosis doesn't really matter as long as a child is getting help but I actually feel like we didn't come up with the RIGHT road map for our DS until me knew what was really going on. He has a language disorder so now we know we have to focus on that above all else since it is the root cause. Without that knowledge, we might still be working on the wrong things. So I guess I would say that, if you do think something is going on, you should really try to figure out what is up.
If I were you, at this point I would list what I see as potential issues that I would want to work on. Then think of the kinds of help you think would address those issues. That can be the foundation for what you think would be a good IEP. If the school disagrees, ask them why. Closely examine the issues they believe should be focused on and, if you don't agree, follow up with them. Don't be afraid to be an aggressive advocate (you don't have to be mean, its possible to be firm without being rude).
So, for example, in our case the preschool listed that DS would be able to sit for 20 minutes during story time in their proposed IEP. Well, first I don't think it is developmentally appropriate to expect 3 year olds to sit for 20 minutes. But beyond that, this is a great example of working on the symptom not the cause. DS won't sit for a story because he doesn't understand it. So yes we could "train" him to sit still and "listen" but what we should really be spending time working on is his comprehension. So I would much rather that IEP goal be about working to increase his comprehension of basic words. Hope that distinction makes sense?
Anyway, I also think the ADOS is a terrible test. Kids who are not as complaint get higher scores. Children with language disorders are regularly misdiagnosed by that test. If you think they school eval is missing something or misunderstanding something about your child, say that to them! Talk to them about your concerns. If they respond well, then great. If not, then you have rights and should work with an advocate to make sure your child is getting the kind of help you want.