Are you in a clock-wise orbit? If yes, just wait until your ship is at its farthest away from Kerbin, so that you can draw a straight line between it, the Mun and Kerbin. Then, you just burn prograde until you leave the Mun's SOI. This way, you also kill the orbital velocity you gained from the Mun, so you'll get a future Kerbin-orbit that will make you fall straight back home.