If I used the wrong terminology in my english exam will I be heavily penalised? It was A level...I'm worried!?

I think I used the word 'interrogative' rather than 'imperative' which does change the meaning somewhat! I'm not 100% sure that I did make this mistake, just post exam dissection! Will this dramatically pull down my overall mark? I have worked so hard for a good result I am so scared that I might have actually messed up my Uni chances for one silly word! Also, as a by the way- does anyone have any good sleeping methods for post exams? My brain doesn't seem to know how to switch off! Help please! Thank you!