Help! Stubborn blue marking pen

I've just created a holiday table runner to raffle off as a fundraiser for a local civic group.  My water soluable blue marking pen (which has never behaved like this before) simply refuses to wash out with sprayed water.  It disappears when I wet it, only to come back when it's fully dry.  Any hints/advice? 

Hi Have you tried spraying hairspray onto the pen mark. I have used hairspray on pen/ink marks and I always use hairspray before I wash the item. Hope this helps Jackie.