Depends how well you learnt everything. I'm guessing completing the syllabus means just having gone through the textbook and done the questions etc.
There's probably the danger of getting complacent with what you've done and taking it too easy next year because you've "done the work", so be wary of that too.
It also depends on how in depth you actually went, I'm guessing to have finished all that in such a short time frame, you didn't sit back with concepts and explore them really deeply and really understand everything inside out.
But yeah, take a break and go outside. Even when school starts, you really do need to maintain some kind of balance between studying and 'having a life'.