I'd shorten the chain, but first I'd go ahead and ride it until it needs to be adjusted. You won't cause any problems running it full out and in fact, running it too close can cause problems with mud jamming between the tire and swingarm. I took links out of my YZ450F's to scoot it up and turning improved a little, traction seemed to improve, and mud got jammed. Good trade-off in normal conditions, IMHO, but not for mud. Anyway, let the chain stretch, then take some links out.