I would wash it in my washer and only put in usual amount of detergent. Maybe rinse it twice and dry it.
I use cold water tide, cold water and dry on low. You may have to pull out and reinsert quilt until dry.
I spread on my bed or on my glass topped dining table overnight.
Never had a problem with washable Crayola markers not coming out.
By the way that is a gorgeous top. Perfect piecing.