UT Austin is a really good university. If you are auto-admit at UT-Austin, then you know that you will be at a great university when the time comes. You just do not know which one. To me this should take a lot of pressure off.
Otherwise “top 20’s” are reaches, but IMHO reasonable ones. You are a very competitive applicant.
Apply, and see what happens.
Also, pay attention to your budget. Pay attention to what YOU want in a university, and do not attend a “top 20” just because of the ranking.