In my Mocks, I only revised a few weeks beforehand and so got 2 A and with the rest being all B and one E. In my real GCSEs I revised for months beforehand and managed to get 1A* 7A, 2B and a D (P.E where over half the year got C and below).
As long as you put the effort in it will all be fine. I could have got at least 3 more A* but I didn't put effort in for things such as Controlled assessments, so although I got A* in the exams, Controlled Assessments brought me down to A, so my best tip would be to take all coursework seriously.