Everytime I seem to get going fast, I end up flat-basing and catch an edge. Any tips on how to stop doing this?
Slow down either lean down hill or pull up on the rear, which ever way your mind makes it work.
If you are just learning and traversing a lot with the board perpendicular to the slope, both feet have to work hard to keep the down hill edge up, and this should be your primary focus when sliding down perpendicular. If it is not, you will catch that edge.
If are moving in a manner where you have a front foot and rear foot, and you get going too fast and start to get scared , you will learn on your up hill foot out of fear, if you you lean on the uphill foot, that foot will start to fall down the hill in an unexpected and manner, it will fall either toe or heel side, whichever one is bearing the weight. If you have the weight on the uphill toe, the board will come around and catch toe side and face plant. If your weight is on the heel, you wont see it coming and you'll end up on your back looking at the sky.
I learned to do a jump whenver I space out and my rear foot gets a mind of its own. It is usually on a very flat area and I start to relax, stand straigt up and start looking around for the rest of my group.