Hi Mouth... ha ha funny username
Judging from the pics I think the seam has to go the other way. Across the bottom of the purse. From front to back, not side to side.
Here's a pic of the bottom of a bag I made for my grand niece...
Here it is before I did anything to shape it. It is a soft bag and it was just flat with one seam all around.
What you do is, turn it inside out and grab the corner and make a flat place and sew straight across. Then lay that flap flat down against what has now become the bottom and sew the seams that you see there in red. Oh and I did all that before I lined it...
Here's another pic of the bottom of it. The sides are poking out only because it's laying flat and the bag is so soft... and even though it's really soft it stood up all by itself after I did that to the bottom.
I should have taken a pic of the inside seams so you can see that... If you don't get what I'm saying don't feel bad about saying so. I'll sew a mock purse, take a pic of it and post it. Someone here will have some more answers also I'm sure. It seems confusing at first I know, but it's easy when you get the hang of it.
Keep us posted on your project. I love the colors and I'm sure it's going to end up great!