Don't worry, the first service is supposed to be at 600 miles, not 500 miles.
So, with 100 extra miles to go and a 20 mile per day commute it will give you (100 miles) / (20 miles/day) = 5 days (or, a week, assuming you commute 5 times a week) extra time ! Well that is a nice coincidence, isn't it !
You could also download the instruction manual and try to do several things yourself. I already had a wrench set, and to properly work on the bike I bought a torque wrench (Sears, with dial, I think it was around $25) and a feeler gauge (was around $8). Chain cleaning, oil and filter change, valve stem clearance checking and bolt torque checking, it took me a several hours but I managed to do it all myself. The tool set with the bike is very handy too, for instance for getting the spark plug out. And I'm sure it will all take much less time next time around, at 3,000 miles. which is soon I hope.