I want to fuck my younger sister her ass has gotten so fat 😩😍

So for the past few months, I’ve been fantasizing about fucking my younger sister cause she’s growing into such a beautiful young woman body. Her ass is so fat. Today while we were watching movies, I put my hand under the blanket and slowly, but surely started putting my hand closer to her pussy. I could just feel it getting hot around us. I feel like she keeps telling me to move, but she wants me to keep going because when I do it again, I keep getting closer and warmer to Wright where her pussy is. Today I got really close and almost rubbed the outside of her panties through her pants. Tips to get her to give me more? I feel like she wants to, but it’s scared/thinks it’s wrong.

She is 18 I am 21