I had to join TN parents so I could reply to this. (I'm in PA - not TN.) It took me a while to get to a screen where I could write a reply. You might not get a lot or responses because of this.
IEP services are based on data. This data comes from the school evaluation showing that the student is lagging in an area when compared to others their age. What I've seen & experienced is, with ASD, students lag with social skills & pragmatics. I've also seen where the schools aren't assessing these areas. So they do an eval & it shows there are no needs because the areas you see issues aren't tested. This happens because parents don't speak 'school' and don't know what to ask for. If you have concerns with academics (because of the score on the ctap), ask for the school to evaluate that area too.
You need to look at the school eval. If it's under 12 months old, the school will not do another eval. If they missed an area of need, you can ask for an IEE at school expense or you might be able to get the school to test the areas they missed the 1st go around. Have you provided copies of the outside evals to the school? Did you meet to discuss them? Sometimes a school will take an outside eval and provide services based on that rather than ding their own eval.
If the 504 isn't working, you can request a 504 meeting and add accommodations. Communicate with the school in writing so you have a paper trail of what happened when.