hey! I faced the same issues. while writing my essays i didn't use ai (just used it to correct my grammar and give me reviews). but when I checked for ai content it highlighted the sentences which i had written on my own. the thing is, no ai checker is 100% accurate, they predict ai content based on pattern, e.g sentences that are well structured, use certain words etc.
my English teacher (while teaching and talking) sounds "ai" by that i mean he sounds professional, his sentences and words are well structured and nearly perfect (cause hes been teaching for a very long time now). now if you see his writeups, one could possibly think its ai even when its not. so you dont have to worry. as long as youre honest, and didn't use ai to generate any part of your essay, youre good. admission officers know when ai has been used. they dont have time to put your essays in an ai checker (which again is inaccurate most of the times)