I love to make bags! What I don’t love is turning out the corners. There are tons of tools; I’m a fan of the skewer myself. I’ve found when the bag has lots of interfacing, it’s even harder. My solution, dampen the corner! You don’t need to soak it, just slip it under the faucet for a second.
Wet fibers are more pliable. But this can work both ways, don’t jam your seam ripper in there and accidentally rip a hole! You’ll be able to work out your corner easily once it’s wet.