As you complete a topic and move onto the next, i would recommend doing the questions by topic from the physics and maths tutor website. Since i don't do biology i am not too sure how much content is in the specification (although i have heard there is a lot of content).
Personally, i think by doing the questions by topic will allow you to identify your area of weaknesses for that specific topic. As a result, you can save more time as you will spend less time revising that topic as you will have pinpointed where there are gaps in your knowledge given that exam season is getting close now.