When are you planning on taking your test?

I think it would be wise to go over your errors and do some thorough analysis on why you got certain questions wrong. Take a log of your errors and try to parse things like question type and subject matter.

When you get closer to your test, I would think about re-doing the difficult questions in the book (tend to be toward the back of each section).

Good luck!

Think about when you're going to take your test. If you've done all 800 problems, and you don't feel ready to take the test, then you didn't really study those 800 problems as well as you need to.

Remember that your improvement doesn't come from just doing a lot of problems. Your improvement comes from studying and analyzing the problems (both for themselves and for your own strengths and weaknesses) after you do them.