Being that you have everything cut, the best I can suggest is to continue on, pressing regularly with Best Press. It will help to "seal" the edges and minimize the fraying.
You may be surprised how things will change with the stitching and Best Press'ing as you go.
Hindsight is always 20-20 .....
One of the reasons for pre-washing is to shrink fabrics, which can tighten up the weave and minimize fraying. Using Best Press post-wash for a good press before you start cutting really does make a difference in the fraying as you work with the fabric. I have seen fabric that was fraying terribly become quite controllable with next to no fraying after.
Good Luck!