Love the colors you picked. You did good. Lone Stars are very hard to get the points all perfect. Many seasoned quilters wouldn't even think of tackling a Lone Star. So give yourself a big pat on the back
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It looks like it lays flat, not easy to do with a Lone Star, but it's just off a bit. I've done several Lone Stars. The most important thing is to keep all your seams exactly 1/4 inch or it will throw off the points. Once you get off it keeps going. Looking at the back the diamonds will seem different in size due to the seams being pressed over. There are many bias cut seams to work with, which isn't easy. I spend more time pinning & pinning & pinning than sewing when making a Lone Star. You did good
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I tend to be picky, so I'd rip it in half & sew the center seam again. That would make it line up better to the edges.
If you aren't picky, then just open up the center red diamond seam. I'd go about half way. Place a dot 1/4 inch in each center seam (L&R sections). Match up the dots & pin, pin, pin. Then sew again, easing it in. Then you need to un-sew the seams that all join the points in the center, back to the main 1/4 inch seam. Just a few stitches on each point. Then press them flat in a swirl. That should make it lay flat.
The outside edge is off quite a bit. If you don't want to rip the center seam out & do it over you can try to square it up. From the front measure from the center seam across to the edges & see how far it's off. If it's not too much I'd lay a long ruler across from corner to corner. If you can keep enough seam allowance at each star point & just trim off the rest. Make sure you measure twice, mark well, measure again & cut once.
When you go to add the borders, fold them in half, mark & pin from the center seam out to the edges.
Again you did good.