yes, i would say to do 1 or 2 past papers for each subject and then target your weak areas. i highly recommend using the website 'MME' (maths made easy), which gives notes and short video clips and then practice questions and exam questions for each topic, for your maths and science subjects as well as corbettmaths for maths, where you get worksheets and mark schemes. but please remember that these are mocks, and they will not determine your place in college, only your real gcse's but nonetheless, try your best and tyr not to stress too much.