I am close to 20 years old and i'm 226 pounds. how much fluoride should i not swallow?

None....: You should not swallow any fluoride, it's not meant for that. Over the counter Fluoride rinses are designed to work by rinsing aka topically applied, you don't nor should you swallow it.

Do not swallow it: Acute Fluoride poisoning, which occurs at doses as low as 0.1 to 0.3 mg per kg of bodyweight, generally presents in the form of gastric pain, nausea, vomiting, headache, dizziness, and flu-like symptoms.

A lot: It is perfectly safe for any adult to swallow some Fluoride like when you brush your teeth, use mouthwash or drink healthy amounts of water. It would take several tubes of toothpaste or an entire bottle of dietary Fluoride supplements to make you sick, and then you would throw it up before you could absorb a harmful amount.