Can you sew at all? It seems any curtain is going to have to be altered to the shape of that wall. Not hard, but you will need to sew.

What I'd do is get a clear glass/acrylic/pvc panel installed to the right. You want to leave some room to get in and out of the shower. You might be able to to do sliding panels, and won't need a curtain. Otherwise, if you have the head room, lower the curtain rod to make it straight (you'll have some room, given that the end of the panel will be further up the slope.

In the absence of that, get a shower curtain without a linear pattern and hem it so that it is straight. Your current horizontal stripes emphasize the fact that your curtain doesn't hang straight. You can buy no-sew iron-on tape for hemming. How well it will work in a bathroom, I don't know.