Selvedge usually shrink differently because it is more tightly woven than the rest of the fabric. You don't say how many blocks have the selvedge on them. If a lot and depending on the use of the quilt you might clip the edge threads on the selvedge to release edge a bit. Uusally it is the first thread on the edge that shrinks the most. It also depends on the length of the edge. Clipping the first one or two threads in a few places probably will take care of it.