Here is a solution that works great on pencil marks. Maybe it will work on your markings.
Make a solution of:
3 oz rubbing alcohol
1 oz water
3 or 4 drops liquid dishwashing detergent
Place in a squeeze bottle and shake well. Wet the corner of a rough washcloth with the solution and rub over the pencil markings. Wet a second cloth with clear water and wring out; rub over the treated surface to rinse. Let the quilt air dry. Lines will disappear entirely when the quilt is dry. Heavy pencil marks may, however, require a second treatment for complete removal.
Submitted by Helen W. Rose, Nauvoo, Alabama