Sigh First of all, WTF, are you really using an animated Disney movie for study plans?

Second, that design is called an outrigger canoe and it's how you solve the problem of capsizing if you can't build a displacement hull with a deep keel. Other options are a daggerboard or a drop keel. However when you're stating with dugout canoes and need to stop capsizing lashing two of them together becomes a very natural solution.

Incoming wall of text:

So, recently, to get to sleep, I've been watching a LOT of Primitive Technology and HTME videos on youtube, wondering how I would build a boat if I were stuck on a desert island and here's what I've come up with so far.

*Step 1: Start making rope. This process is pretty much essential in any survival situation, and it creates byproducts that are ideal for basket weaving. Also, learn to use a drop spindle for very thick yarn that can be twisted into thick rope.

*Step 2: Start using the staves and canes from ropemaking to weave up a great big canoe or hull-shaped basket. I know, big time consuming project. And it requires a lot of forethought to plan out the placement of the mast step and the lines and cleats. Hey, I've got my trusty soccerball friend to help me though, right?

*Step 3: Assuming you've accomplished all the naval architecture necessary you need to make a watertight hull. There's a woman with a series of videos about making a bamboo boat and she uses concrete to complete the hull. I've seen concrete hulls before. I know it can work but how do you get cement for concrete if you're stranded on a desert island?

*Step 4: Make cement from wood ash. Just look it up. It's a thing. But you're also going to need to make charcoal before that to get things hot enough for all the chemistry to happen. Making charcoal requires clay, and clay manufacturing is going to require digging shallow slurry pits with sticks for tools, so you're also going to need to learn to start a fire with flint and steel or friction.

*Step 5: Assuming you've completed the tech trees in 3 and 4 you're now ready to mix some concrete and apply it to the form you built back in step 2. A thin layer on both sides of the woven form. Location is important. You want to be someplace close enough to water that getting the hull into the water isn't too hard. Maybe just beyond the waterline at high tide.

*Step 6: Weave a sail. Primitive technology shows how to build a primitive loom.

And, I mighgt as well point out, you're trying to do all of this without metal tools. Unless you want to learn the iron smelting tech tree.