You can do a few things to help with turning:
First is to attach the rope to the tie of the skis, or run them through eye bolts on the tips- that gives you more leverage to turn, and the lift you apply to the tips lightens the front and helps it skid
Next, you could round off the edges. The metal edges are for turning while the ski is bent, and aren't useful in a Smitty. That won't help if the snow is deep though.
Finally, load the weight to the back, to lighten the tips. And for sure, the lighter the sled, the easier it all will be...
You also ned to make your Smitty wide enough to be stable with the side loads of turning. Turning is when things can tip is too narrow and tall.