So long as you prepared as usual for immersion, with your final preparations at night shortly before immmersion, and visually inspected yourself before you immersed, we can assume that the pen marks were not present when you immersed. Accordingly, your immersion would be considered valid.
Even if this were not the case, there would be room to consider your immersion valid, given that a pen mark has no independent physical substance, is presumably very small, and is presumably not something you or most women would mind terribly having on your body. You need not go back.