hi hi! for starters your parents are kinda dumb for that, you can definitely be a high achiever and autistic? it's literally one of the autism stereotypes that we're super good academically, and even if that stereotype is often suuuuper disconnected from reality, the point is that bad at academics ≠ autistic. autistic people can be good or bad at school! it depends on the individual and the school honestly.

I'm not entirely sure how to help with this admittedly because I was diagnosed when I was 11 and never had to go through any sort of discovery journey with autism specifically. I think it's probably like researching any disorder though! read up about it online, both from more professional academic sources and first hand accounts because frankly, both are biased in different ways and you'll end up finding the reality of the disorder to be somewhere between the two. psychiatric resources are often written by people without lived experience and can be detached and not account for super common experiences, while accounts from the community can go unchecked and end up spreading misinformation that has no basis beyond "yeah that sounds right to me" and may even actually be describing a comorbidity (most commonly CPTSD in my experience) instead of autism itself.

though I will say, I advise against rushing into getting specifically a diagnosis for autism. seeing someone who you can talk to about it and get their opinion (like a counsellor) is good absolutely, but in many places, an autism diagnosis can outright bar you from access to certain things and lead to you being oppressed. you should ONLY pursue a formal diagnosis for autism if you need access to the real world accommodation that comes with it! self-diagnosing or simply being recognised as likely autistic by a therapist is frankly enough in terms of if I think you can call yourself autistic and be welcomed into the community. the emphasis on needing professional diagnosis is outright dangerous, so please take into consideration if it's something you need (for school for example) before pursuing that. I was "diagnosed" when I was 11 but the papers weren't properly put through for 10 years because I didn't need access to any accommodations as a kid (like speech therapy and such) and I think that ended up being a good way to go about things. also here at least it is SOOOO insanely expensive to be diagnosed my god.

tl;dr: do research the same way you would any disorder! by talking to autistics and by looking into more objective academic sources. don't rush into explicitly a diagnosis because it can be dangerous, do so only if it benefits you. aim instead to talk to a professional about your traits and see their opinion/be recognised by them! a good therapist will probably understand why an outright diagnosis isn't something you might want, so.