First off, it's only been two days, so don't worry too much. You WILL get it if you keep trying.
With that said, you may be rushing the edge change or trying to change edges whist sideslipping. If there's ANY sideslip going on when you change edges, you WILL catch your edge and fall. If your board is scraping loudly over the snow/ice, it's probably not safe to change edges. Remember to initiate the turn with the front foot, then follow through with the other.
As fredericp64 said, bending the knees and ankles is important, otherwise it's like trying to snowboard on stilts. Think about resting your shins on the front of your boot to get the ankle flexion right.
As for riding switch, it's like learning all over again. I'm getting to be an alright snowboarder and run blues without speed checking, but you better believe I come back to the easiest greens when I want to practice switch. For extra tardedness, try skating around and catching the lift with the wrong foot out of the binding.