There are several reasons that rice might stick or burn. The two main reasons are not adding enough water or cooking the rice for too long. Using a quick release, instead of a slow, natural release can also cause rice to stick to the bottom of the pot. Rice might also stick and burn if you leave it in the pressure cooker for too long. Don't let cooked rice sit in the pot on the warm setting for too long. Also, if you're using a 6-quart (or larger) Instant Pot, then cooking only 1 cup of rice might make it scorch to the bottom. You'll have better luck cooking at least 2 cups of rice at a time.