I'm in year 10 too and expected to get either 8s or 9s. My sister did her Gcse's last summer, and said that she wish she'd started revising sooner - some of her friends started in year 10 and found it a lot easier when it came to year 11, as it meant they had notes from topics they'd pretty much forgotten by that point. it also meant that they had less to learn anew, as it was easier to keep on top of and remember. Although she didn't get as high as she reckons she could've had she satarted revising earlier, she put in loads of revision when it got to year 11, which meant almost every night she was revising. i have spent the weeks off starting on revision notes and going over stuff I've done this past term which i know i wont come across again until my exams. I would say to definitely start revising now and doing about 2 hours a night until you're completely caught up on notes in all your subjects.