yes that is why the gcse course is two years long
no you dont revise EVERYTHING, your tacher should tell you the things that they will/wont test you on, but thats why you have modules and it should be easier to stay on top o the work rather than do it all at the end.
You need to revise some parts of the year 10 modules. Not everything!
There are 6 topics from year 11 you need to know they are:
Patterns of chemical change
Inheritance and selection
Structures and bonding
Waves and Radiation
For year 10 you just need to know some information from each of the 6 modules, our teacher gave us 6 papers he wrote himself telling us what stuff we need to know, the information also goes into detail so we don't have to revise the year 10 stuff from books.