Okay, the answer is learn to keep going by yourself so you stop worrying about it.
Firstly, do it when your mom is out and start learning that making noise is more than hot, it actually makes your orgasms feel even better as you let it out.
Secondly when you do it and have to be quiet, dont’ completely stop rubbing, just lighten up the pressure. Move your fingers off your clit and just rub the whole area as you’re cumming, or grind the palm of your hand up and down over your mound. You can do less and stop it being ruined.
Lastly. Don’t stop doing what you are doing sometimes. Ruining your horny little cunt and leaving yourself wet and horny is hot as fuck.