Just do read -> example exercise
- understand the example exercise?
yes --> try a few normal exercises (one of the first, that's short and easy. Another of the last that's often a little harder)
no --> watch a Khan Academy video on it, then do the exercises
Anyway, don't panick. 3 days is a really long time. Just make sure you really use it and don't procrastinate. Don't go on all night, I have experience with doing that. During the night you can often still going, but you won't last the second day without sleep. You lose concentration and just don't remember things.
Put your phone somewhere far away so you can't get to it. Divide it into multiple parts (if that wasn't done already) and take a break everytime you've had a chapter and 1,5 hours or so have passed. Get something to drink or take a little walk and continue.
Once you've made it through all chapters, hopefully you have one of those test-tests or whatever they're called in english. Pretty much an example test that has been made available that's representative for an actual one. Do that if you have the time. Then check the answers and see what things you should learn better for.