Wavy edges on table runner

[alicaz]

Ok, so I made my first quilted table runner - it's a gallery of imperfections (don't send the quilt police, please), but I learned a lot of "what not to do" things on it - like that good quality fabric is really important (the white I had at home and used is way too thin) or that I REALLY NEED a binding tool...

There is one more thing that's bugging me and don't know how to avoid it in future - the edges are kind of wavy - don't lay flat on the table? is that normal? if not, what can I do to have nice straight flat edges?