The first modification I made was to the shape of the thing.
Those big square bites in the center? That gives the purse depth. (I saw how to do this on a sewing show. I can't find a good explanation online, but this kind of gives the idea in pictures.)
Once the form was knit, then I sewed up the seams.
The whole thing is kind of a mess, but that was deliberate. I made it big and open so that it would felt. Once the form was finished, I put it in a hot machine wash with towels until it felted. Then I attached the strap and got my final product.
I had to do a little tweaking. The strap was too long, so I trimmed it down. Then the magnetic closure wasn't attached really well, so I had to take that off and redo. But as of this moment, I'm happy with it.
Although, it's a bit larger than I like. I may have to make another one.