I recommend playing in full screen just because it looks better, but it plays the same either way. The reason you are level 20 is because you killed flowey before you approached sans. Also, I know the color is red, not crimson, but I thought crimson sounded better. I am trying to fix the slam animation, but i'm hiding it from view until then.
Thanks to: Toby Fox for Undertale loganvcairns for the original project scratch for existing my mind for being able to think of this