I might fuck my teacher after school

it’s 14:16 as I’m typing this. school ends 14:40. I finished maths and my teacher (she’s in around her 40s-50s), let’s call her miss b. she asked to keep me for a second at lunch. she said to me she’s very proud of how I have improved, and I should somehow be rewarded, and I noticed her bite her lip slightly and look down. what should I do?