Well, the good news is that you're home and can try several setups. First off, the cart needs to stay on the canoe. If it slips off the end, then you'll need to involve a thwart. Can you lash or tie each end of the cart to the thwart on that side?
Most of the time when the manufacture says that the cart will fit all these different boats, what that really means is that you are going to need to develop your own system to get it to work on your canoe. Depending on what you have to attach to on the cart, I find that a good lashing will secure just about anything. If you like the idea of belts, then look at what you have and where belts would work, you're not limited to one, most hardware stores sell nylon belts and buckles, so you can rig it anyway you like.
The cart needs to hold on but your not going down the freeway with it so what the heck, pull it around and see if it starts slipping. If you were to pick any ten folks here and ask them to attach the canoe to the cart, you'd see ten different way of doing it but I'd bet that all ten was would work. Have fun figuring out what will work for you.
Best Wishes,
Rob