The first GCSE exam is on Monday 16th May, so you have four weeks and five days (including today) to revise. Taking out the weekends (during which you said you couldn't study), that's 23 days. At three hours per day of revision time, that's 69 hours. With seven subjects, you will therefore have 9.86 hours - about 9 hours, 50 minutes - per subject.
I would have a look at the
TSR Study Planner, and enter the times that you can study alongside your exams. I know you said that you aren't great with timetables, but if you're worried about getting everything in then it's a really great way to make sure that you do!
From the above, you can see that you have just under 10 hours per subject, so plenty of time!
I would then suggest going through and counting the number of revision sessions you have per subject, and then determining how many topics you will need to cover. Divide these up between the sessions in a way that you see fit.
Once you've done all of that, you will have a pretty, colourful timetable that will make you actually
want to revise!