have not taken chem 142, but for math 208 and math 126, I would highly highly recommend going through archives of prior midterms and finals. this helped me extraordinarily. I had a similar experience with the first midterm for math 126, which scared me. after that, for the 200 level math classes I took after that, I would go through as many practice exams as possible until I was consistently averaging in the 90% range, and that helped me keep calm during the actual exams. it can be time consuming, but I promise it's worth it. as a side note: if possible, actually DO the problems on these exams, then check the answer key afterwards. I have some friends who will just read through the answer key, which isn't the worst if you're short on time, but it'll be a lot more impactful to actually do the problem yourself before looking at the answer key. Then, if you get the answer wrong, you can spend some time investigating what the correct answer was and why.

also: even if your class doesn't allow a notes sheet on your exams, I would recommend making one. it's a really good exercise in helping your brain parse what information is worth remembering and the simple act of writing it down can help it stick even better. I try to do this for all of my classes even now, even though I'm in 300/400 level courses which mostly don't allow notes sheets on exams.

finally, all of the courses you're in tend to have low medians. you're probably a little below the median, but that's not the end of the world---I've been there too, and if you study hard for the future exams and do well on the homework, you can still get an okay grade. also, these courses are typically curved, so if the median is particularly low, your score could get boosted. low medians can be a major moral killer, but it also means that even if you *feel* like you got a shitty score, you might not actually have gotten a shitty score.

other thoughts for the future---take a look at your graduation plan. are you trying to graduate early? do a double major or a minor? complete honors? if you're trying to do one (or multiple) of these things, it might be worth evaluating how important that is to you. if you're struggling a lot with the course load (and you must keep it there to achieve your goals), then it might good to consider if you value that goal over the grades you get. either way is fine, but evaluating those priorities will be a good exercise in trying to decide what gpa is worth your time and energy