Good day there. I don't believe that there is anything wrong to masturbate when you have your period. Can masturbation delay your period - the answer is no.
I think that masturbation doesn't control any hormone in your body, so you should not be scared. You should not panic if that happens - maybe there are some other factors. Don't listen to a story of other girls, every girl has a different body.
Also, it depends on how tall you are and how much do you weigh.
You should talk to the gynecologist and ask about any of your concerns.
He keeps the best answers.
GL
My period was heavier than normal when I masturbated untill the day it actually started. But the two may not have been related to each other. If I did masturbate while on my period, I did it only right after my shower as I had washed the days blood off/out. But what happened to me may not apply to you.
There's only one way to find out if you'll bleed heavier, and that is to try it. Everyone is different. If it does get heavier and you don't like it, try to avoid masturbating the next time around.
Good luck.