You do need to make sure your fuel system is not leaking even if that means taking the whole thing out of the plane for examination. The plug in the front of the tank could also be loose or it could be too tight and the tank may have split at a seam. Could be a pin hole in a piece of tubing or everything may be OK. You DO need to find out because extra fuel running about in the plane will quickly destroy the wood. NEVER leave fuel in the tank when you are done flying, always drain the tank.