First of all, if you are asking this question, you have to be using too much gel. You just need a tiny bead of gel to cover 2/3 of the front of your tooth only. And you don’t need gel for all your teeth. Focus on 9-10 spots on each tray.
If gel is oozing out of the tray, you have used too much gel and you may hurt your gums. You should take the trays off, rinse your gums, and try again.
Now, the gel is not a toxic material but it is a chemical. If you accidentally swallow some gel, it is OK but we don’t recommend swallowing any chemical.