Is the mole concept important for unit 3/4 Chemistry? If I get bad for this SAC, do you think my teacher is going to make me drop Chemistry??
Yes and no.
If you don't understand the mole/stoichiometry by your first unit 3/4 SAC, you will have trouble. If you do bad on this SAC, though, I do not think your teacher will make you drop Chem.
The mole is a difficult concept to understand - believe me when I say, you're not the only person who has struggled with it. It's an entirely new way of thinking and quantifying elements, of COURSE you'll struggle at first.
The mole reappears in unit 2 when you cover stoichiometry - if you're struggling now, do your best to try and wrap your head around it, but know that you'll have a second chance.
I also suggest checking out various YouTube videos, Khan Academy videos, vTextbook, etc. What about the topic are you finding particularly difficult, if you don't mind my asking?