Wow, this is great news.
If you are going to be planing (i.e. wind > 15 knots with your 6.7 NP Tempo) you need to retract the centerboard completely.
The reason the board is "railing up" and giving you control "issues" is a direct result of having the center board down. It created too much lift, and could potentially break off.
No one uses the centerboard when fully planing as it's much easier and faster to sail upwind "on the fin".
Your 56 cm Drake fin should take you upwind very nicely, but you will need to change your technique a bit as you will be "foot steering" (i.e. tipping the board upwind (heels down) to go upwind and tipping the board flat to slightly lee rail down to head downwind.
At some point you will get fully hooked in, and have your sail raked all the way back until the foot of the sail is parellel with the top of your board. When you reach this point, the steering will change again, but only slightly. To go off the wind (downwind) you will push down with your toes to roll the board quite a bit to leeward (lee rail lower than windward rail) and un rake the sail slightly.
To sail upwind, you will roll your board very slightly lee rail down and push across the top of the fin very hard with your back foot. Maybe even pull upwind slightly with your front foot.
Then you will be going upwind completely on the lift (horizontal) from your fin.
With the daggerboard down, you use rig steering. With the dagger board up you use footsteering.
As far as the footstraps, you can open up the outer cover, and pull the center strap up to fully disengage the velcro. Then pull up on the footstrap to get the center strap to pull around the metal bail at the front of the strap. When you get it adjusted to your foot size, re-engage the velcro on the center strap and close the cover.
If the footstraps are too narrow, move the footstrap screws one hole wider. You can run the center hole in the back and the front hole in the front, or vice versa.
I run all my footstraps this way on all my boards.
I like to be able to twist my foot slightly in the strap to put my heel more forward or back but I can cinch down the adjustment so my foot is retained on the board with just my toes showing on the inboard side.
Please retract your dagger board when you think you might get planing.....
1/ To prevent the daggerboard blade from breaking off.
2/ To give yourself the best possiblity of planing with good control and good speed.
Hope this helps,