I always just measured the side rails on the ski and added the top and side portions together to get a straight length (not the plastic pieces you removed). Then just cut the strip of turf that wide. When you go to install it, line up the edges on the top first for cosmetic purposes and fold it around the bend. Trim the excess. The one hard part is the very front of the ski since that's got such a tight turn but the principle remains the same. Start at the top lip and work it around... Heat is helpful on the sides but absolutely necessary on the front.
edit... Patience is your friend when turfing. Coat the ski and turf once, wait 10-20 minutes, coat turf and ski again, wait 10-20 minutes, finally lay the turf on the ski. Anything less on both number of coats and wait time will end in disaster either immediately or soon after.