i also took series and differential equations, and it was so messed up! i left the last question blank. so... doing good in everything else does not guarantee a good grade in paper 3.
about regrade. if it's not too late yet, i don't think you should do it. my reasoning is: in maths you either get a right answer or you don't, so you either get that point or you don't. there is no room for different interpretations like in english or in group 3 subjects, where a lot depends of the examiner. in maths, everything si quite straight forward. and.. how could you calculate that you should have gotten 34 points? you don't have the markscheme, and you don't know for which lines in the answer exactly they give points. but don't missunderstand me. i do sympathise with you, because we all know that ib is not always fair no matter how much it tries.
so... if you still think that you really want that 7, then go ahead and get it regraded. but i don't think there's a significant chance that it will get regraded.
ps: what is this thing about added points? i have never heard of it, and i am almost certain that it's a rumour. clarify?