Do your mocks really reflect your actual results?

I am sitting 2 AS levels (chem and physics) in October and i am doing self study, i do mocks and correct them by myself. I normally score 65-72/80 in mocks. However it might be due to me being too soft to myself so i deducted fewer points. Also, in the next few weeks idk if i will be able to study really hard sooooo do yall think im able to get an A if the exams were tomorrow? Im getting lazier and lazier these days i cant get myself to study.

Are there cases where people got a B or C even when they constantly score 70/80 in their mocks?

Btw im not sure if this is acceptable but it would be great if someone is free to mark my mocks, thanks!