It can take a few tries to get it right, and you won't know until you drive it. You may also find that things change a little once the transmission warms up.
As you probably noticed when you loosened the screws, everything is free to move at once - the shifter body and the silver 'stop plate' underneath it.
The stop plate is the key.
It's the relationship of the stop plate to the shifter body that determines how far left or right the shift lever is free to move. Making fine, final adjustments is usually a case of keeping the shifter body from moving while you nudge the stop plate left or right, a very small amount.
Another confusing thing is that the stop plate is BELOW the ball while the end of the shift lever you move is (obviously) above the ball. So, to get the lever to move just a bit more to the left (for example), you need to slide the stop plate just a tad to the right (while keeping the shifter body from moving at all).
Hang in there, and you'll find the 'magic' spot eventually.