The next step is to layer it to create the quilt sandwich -- backing fabric, batting, top. If you are planning to machine quilt it, I recommend heavily starching the backing fabric before layering. I find spray basting is the easiest way to secure the quilt sandwich, but other methods are to pin baste or thread baste the sandwich together.
It looks to me as if you may have a problem with the border you added, though. It looks as if the border is rippled and not lying flat with the rest of he top. If this is the case, the excess fabric will probably not "quilt out" and will cause the edges of the quilt to be rippled and wavy.
The best way to add a border is to first measure through the middle of the quilt, then cut the border to that length, pin together at middle/quarters/ends, and then sew.