Tuss, good that you are now putting both hands on your knees. Bad you got hit in the forearm, if I had a dime ....well you know the rest!! Have someone look at you while working the GD, (hopefully another GD user) and have them confirm that you are in the slot and not drifting back over toward the catcher. The reason I say this is, in 'normal' circumstances your left arm should be relatively protected by the RHB, and unless the pitch was inside and the batter moved, you shouldn't be getting hit there with regularity.
So, continue to work on it, don't give up and you will soon be able to call pitches that you might have not been seeing before.