Beautiful colors. Love your backing fabric. My first bound quilt had the same corner problems you did, until a kind soul here suggested watching a few YouTube videos on mitering corners on binding. Once you learn the trick, it is like night and day on the next quilt. I made myself a sample quilt (mug rug size) and started sewing the binding on a straight edge, so I could have it in hand, as I watched the videos to be able to actually do what was done in the video. After I sat a watched some videos, I got out my pins and practiced with them until I could see what needed to happen. (I am slow visual learner and this worked for me.). You do have a good eye for colors on yours, my first was not so pretty.