I used to run cross country. What shoes are you using? I used to get horrible blisters and shin splints until I went to a store called Fleet Feet (In CA)...it was something like that. They watched the way that I walked and jogged and recommended shoes good for me. They were Saucony and cost about $120, however I ran everyday in those shoes for a year with no blisters!

I would say you're doing good right now at training. I wouldn't try to increase your distance since the 5k is soon. I would just keep running what you are. When you get into the race, something just pumps through your body and you don't even realize how far you're capable of running.

you'll do good, don't fret. Keep hydrated!