i was exactly the same. i had a couple of revision flights beforehand so i could practice PFLs and diversions as they were what I was weakest at.
navigation should be fine, make sure you check your time and tell the examiner that you're a bit quick / slow on this leg etc. you fill out your plog and during the last leg you'll do a diversion, so just make sure you have rough wind calculations in mind (i.e. max drift figures) for that leg, and apply them. even a rough calculation is fine, it doesn't need to be spot on, and you don't need to end up spot on top of the place you need to divert to, as long as you can follow where you are on the map.
when it came to the test my examiner was excellent and told me exactly what he wanted me to do. it was a great help - he won't just leave it to you, he may give you a pointer or two, i'm not sure what yours will be like but i imagine he'll generally look to pass you unless you really really f*ck up royally, which i doubt will happen.
i was bad at PFL's too in practice, luckily for me, there was no wind whatsoever when I did my test, so it was a bit easier. you'll do fine, it comes at the end of the test and the landings take about 30-45 mins, you'll do those circuits in no time, all the while the examiner will tell you what he wants you to do. don't worry about it.
the test is about 3 hours long as joe says. drink lots of water and maybe a lucozade sport to raise your sugar level a bit. feel free to take a bottle into the aircraft as well. so many times i've not eaten anything the whole day of the flight and i've got out of the aircraft feeling drained and faint.
when you look back after the exam, you'll see that it was just going over what you've learnt in the syllabus. it's not a strict exam at all. they just need to see that you're generally good at what you've been trained and can handle yourself and are decent at flying. if your instructor didn't think you were ready for your test he wouldn't have recommended you do it yet.