Doubt you'll be able to switch off if that's the sort of person you are.
If you are struggling though, might be worth trying to get a mentor to help you, there's loads of mentoring sites and I think a lot of them are free.
I still actively think about work outside of my working hours but I think there comes a point were you have to think is it worth stressing too much over the little things.
At the end of the day we're a long time dead so make the most of things whilst you can.