im doing compsci at unsw whilst barely getting through 2u (35 raw mark
)
while my degree is definitely not as maths heavy as mechanical engineering, maths at uni is rough... a lot of exercises i'm doing assume knowledge of combinatorics and writing up proofs which i did not know anything about until last week. they do run you through most things you need to know early but they do so at a very quick pace. so it is not impossible to get through maths courses without doing 3u or 4u but just know that you will be in a world of hurt if you don't make an effort to keep up early.
anyways, as uni progresses the differences between those who did advanced and 4u will even out as you gain more knowledge so if you really really want to do mechanical engineering and are willing to put in the work then i wouldn't worry about it too much for now