Stressing over Degree classification?

Ok I'm really confused about working out my degree classification. In my first year I got 61% and in my second I got 63%, however my uni wants to weigh the modules according to credits taken and some were more than other. Does this lower my average? At Uni I recently got 2:2's for my first three essays, is this going to affect my final grade? Am really stressing out and have no idea how to calculate where I'm going to head? I really want a 2:1 overall, someone help me!