Lawrence, it's good you are practicing that strum, it's the basic bluegrass rhythm strum Dave keeps preaching on. I'm with Sylvia, planting your pinky somewhere near the sound hole will help with keeping good position, but it takes discipline. I find myself going sloppy, especially on chords that have their bass notes on the lower (5th & 6th) strings. Alternating the bass is real nice when you get confident, on a G chord alternating between that low G and the B. I think planting your pinky also helps keep your strum more consistent, you will have the proper pick angle and won't "over attack" the strings. There are many different strum patterns, but this basic bluegrass strum is the one to use for our tunes.