What should you do if your lip is bleeding in class and you don't want other people to know?

Try to cover your bleeding lip with your other lip.

Get to a water source as soon as possible and get some drinking water into your mouth. Bring that bleeding lip into your mouth and let the water slosh on it a bit to mix with the water. Spit it out or swallow.

The water will dissolve the bit of blood on your bleeding lip, so no one will notice as soon as you diffuse it with the water.

While your lip may take a few days to heal from that cut, try not to smile too much or stretch that lip, or else the wound may peel and bleed again.