Well, the main thing is to not let it get to you that badly. Depending on how you, as an individual, responds to stress you could have been making the situation worse. I'm finding it hard to picture a situation where the grade of a typing class is going to impact you that greatly (unless, I suppose, you're going to be a stenographer). Bottom line: Relax.

Secondly, If you're making that many mistakes (as do I, so take this with a grain of salt coming from me), then you really SHOULD work on accuracy before worrying more about speed. You're fingers could move at the same pace as someone running 140-170 WPM, but if you're consistently having to erase many of the letters you've already typed, then you could be driving your average down to 80-90 [of course depending on how bad your accuracy might be]. On the other hand, I personally get ~70 WPM, but I've found on the games that I have higher accuracy, I can easily get over 95 WPM just because I don't have to backspace and retype as much. Bottom line: Accuracy is equal to, or of greater importance, than how fast your fingers mood.

Some reccomnendations.
1. I started doing an exercise in Notepad where I just work my fingers individually, tapping all the keys that they should be tapping. it looks something like this:
aqazaqazaqazaqazaqazqaqazaq
xswssxswsxswsxswsxswsxwssxs
dcdedcdedcdedcdedcdedcdedcd
frfvfrfvfrfvfrfvfrfvfrvfrfvfrfvfrfv
bgtgbgtgbgtgbgtgbgtgbgtgbgtg
frtgbvfrtgbvfrtgbvfrtgbvfrtgbvfrtgbvfrtgbvfr

can you see the pattern? I'm just working each finger on 3 keys (6 for index fingers), and I just tap middle, top, middle, bottom, middle, middle bottom. (EDIT: forgot to include that I try to increase my speed, without sacking accuracy, and I don't bother to correct mistakes because I can feel where/when I mess up) I worked all the way across the keyboard one day, and the results were phenomenal. When I was slowing down, I was able to more consistently score higher accuracy, because I knew exactly where I needed to tap next.

Will it for sure work for you? I don't know, but it helped me enough that I thought I would share it with you so you could try (if you do, let me know how it turns out!)

Second recommendation; there's an instant death game mode on this site. If that's going to be something similar to what you're testing on, having more practice with that expectation might be helpful for you when you take actual tests.

I personally don't do that (I just personally don't like it). Instead, what I've done is I will have sessions where I JUST want to work on accuracy so I will play normal mode, slow down, and try to keep my accuracy above my average. If I feel like I've made too many mistakes, I just hit the Esc and move on to the next.

Finally, what I can tell you is that if you were getting upset to the point that you were in tears, that tells me that you doubt yourself. You either doubt your capability, or your capability to improve. What I say to you is, never doubt yourself. That goes for all the other areas of your life. You'll improve with whatever you want, because you can, and you care.

Best of luck.

Thank you so much! I tried your idea and there was an almost instant improvement. I've been working on my temper as well, and am getting slightly better at staying calm when I do poorly.