I found the skills test far less daunting in actuallity than I expected, even when ATC diverted me from my planned route to Whitegate on climb-out due to traffic and I had to do a quick mental recalculation. (fortunately I got it right!) The examiner did his very best to relax me and everything went fine. My instructors had prepared me well and the mock test I'd done two weeks prior to the skills test was actually harder than the real thing. I preferred to do everything in one session as I'd already been waiting two weeks for a suitable day and being December, couldn't rely on weather being okay again for a long time. Another argument to do it one go is that you'll only be nervous once!
Good luck with the test- it's the most fantastic feeling in the world once you've passed it and worth every bit of hard work you need to put in to get there.