Open up the large piece and
Fold the 50" edge over about 26" or 27" (to be sure you avoid selvage being cut into your 'new' piece),
then measure in 25" from the fold & mark it,
then measure 30" down from the top & mark it.
Recheck & verify your measurements.
Mark the cutting lines.
I would pin pin pin the upper & lower layers together at this point to avoid their moving when you move your ruler as you cut them.
Once you've cut, it should open out to 50" X 60".
Just my humble opinion.
Last edited by postal packin' mama; 03-03-2013 at 10:41 PM.