^I can sympathise with the studying the "wrong" stuff. Once you study a few times, you'll find it easier to pick out the key parts to memorise (plus in senior school you know the exact dot points so you have a better guide). Ideally, you should learn everything but I know that's quite hard. It's also best to know the basics of everything. No use knowing everything on one topic in a three topic maths test then 90% questions being on the other two.