I think part of why it's not working because of the yarn. It looks like you have two colors held together? If you do that, you need a plainer stitch pattern - either stockinette, garter, seed or moss, rib, basketweave - something simple. A bramble stitch would work better with a solid color or heathered yarn, but not with two together which makes it look tweedy. That only adresses the stitch pattern, not the curling, though I think you may have too many sts in garter at the edges; that's going to make the sides shorter than the middle. If you use bulky yarn (as in two held together) you probably only need about 3 or 4 sts in garter. And a larger needle.