A mistake that could ruin my academic career

1st year and you’ve stated the tool used and it’s a genuine error, unlikely more than a warning tbh.
Just be mindful that you could be called out for academic misconduct, in which case having a clear timeline of drafts would be helpful.

We receive our grade for it this coming week. I submitted it about three weeks ago, is it reasonable to suggest I realistically would have heard something by now?

So for my very first university assignment (I am in first year), I used AI to do a basic grammar and spellcheck, which the brief said you can do. And even when I submitted it I disclosed that AI was used for basic correction of spelling and grammar. Thing is though, I used Chat GPT for this (stupid I know). The assignment brief said no use of generative AI was allowed, I misread it and now I’m going to be ruined. All words and ideas in the assignment are my own, I just used ChatGPT to do a spell check because it was at the time the only way I knew how. I’m feeling so anxious about this, I’m going to fail automatically for it I just know it… All because of one stupid mistake. How screwed am I really?

The issues with the specific situation have been addressed above but, I would just highlight: using AI for this is a bad idea anyway. There are existing tools already that do this, literally embedded into standard office software.
There's literally no reason to have to use AI for that.

Yeah I know hence why I feel stupid. I just wanted a final proof read before I submitted my final assignment and just for safeties sake. But I regret it now and I feel stupid.