Excellent canoe mate. You haven't been wasting your time at all. It's just that your centre of gravity will be much higher if you use the seat. Imagine if you will, one of those clowns you used to see with a big round ball for a base. You give it a whack and it rolls right over then comes back again, rolling back and forth until it stops. Now imagine the same clown with a flat bottom instead of a ball. Whack that and it isn't going to roll anywhere.
It's a bit like that with your canoe. Because of the amount of rocker, your canoe could very easily tip right over. It isn't going to need much of a whack - probably a gust of wind from the side will do it. Sitting on the seat will just make it happen more frequently. I'd say, get your centre of gravity as low as possible like balast in the bottom of the boat. Kneeling, knees as wide apart as possible and sitting on your heels will probably be the most stable position you can achieve.
If you want to make it more stable (flat bottomed) you could remove all the ribs between the front and back thwart and steam bend them so they have flat bottoms and more acute bends up to the gunwales. You'd need to do that now though before you fit the canvas. If you decide to go down this route, make the transition from round bottom to flat bottom over three or four ribs at each end so it is gradual. That way it won't look lumpy changing from one shape to the other.
The pointy ends can still be rounder as you already have them, but the bit where you will be sitting will be flatter and give you greater stability.
Hope this helps,
Eric
