If you Google on "removing pencil marks from fabric" you'll get many different recommendations. Some of them sound pretty complicated. If for some reason your marks don't come out the first time you wash it, do the search and try one of the many methods out there. Here's one I found fascinating ... and you could try it before washing ...
"If you need to remove a pencil mark from embroidery (or indeed from any fabric), take a small piece of dough from a loaf of white bread, knead with fingers and then rub gently over the pencil mark, which should disappear."
Just remember to NOT put it in the dryer, and DON'T apply and iron until you're sure it's all out.