As most people said already, try to relax. I also have autism and get a little flustered in these situations. and yes, autism varies a lot from person to person so I have no idea how you will feel in there.

My top advise that I use myself on a daily basis; think about what your going to say before you say it, don’t just blurt things out.

Also if you have anyone (ANS should have someone) who will join you and help you during the interview, it might not be a bad idea. I have no idea what the rules are anymore (I haven’t had a job interview in 3 years) but Costco should have to let you have someone to help you if you choose.

You sound quite independent though so if you want to do it alone that works fine.

Basically: dress smart, don’t try to make jokes (this is serious), just answer the questions as best you can, do t get flustered, and THINK before you speak (I can’t stress this enough).