Glad to hear rigging things a little higher helped your out.
As far as getting your board to stay straight ahead when you have your foot over the centerline, that's probably something that you will "straighten out" with a bit more practice and some "muscle memory".
I'd bet you are a little "shaky" still, not getting your foot right over the centerline, and kinda "wobbling" between your front and rear foot.
Any time you put any weight on your front foot, the board will turn upwind, and then you are probably "over compensating" a bit with a little too much pressure toward the lee rail with the toes of your back foot. So you get a little "oscillaton" going.
Just try to even out the weight all on your back foot right over the centerline of the board and keep the weight there until you can fully transfer it up to the boom through the harness lines.
Hope this helps,