Nice work there.One rule of thumb that i can pass on is always where possible bring the 'Shape to the straight'.
Imagine you are sewing up a round bar stool top.You keep the straight border underneath the circle of fabric as you sew....simples.
Dont forget to keep the border under the top panel when you stitch.Its easier.
Also a good idea to put strike marks along the edges as you can see if the next corner is going to fall into place and if sewing a curve too.
I saw on an earlier post that people cant find white piping.PM me for lengths req'd.