About a girl that is really smart and she walks in on this playboy making out with a girl well the girl runs away and he asks her if she wants to fill in and she is completely expressionless and he lets her go well he fell in love with her and tries to get her to go out with him and he finally succeeds what was the name of it?

Except for the making out part, it sounds like the extra chapter in vol 1 of Faster than a Kiss

not quite its a story by itself with several chapters and she tries to avoid him at first.

Stroke Material

need more details...you just described about 1/5th of all shoujo manga...

♪MONSTARR~ will eat all your cookies and steal your bishies~♪ Φ_Φ

Definitely Stroke Material.
Look familiar:
[img]http://i194.photobucket.com/albums/z91/jinxed_you/th_Stroke_Material_v01_ch01-pg006.jpg[/img][img]http://i194.photobucket.com/albums/z91/jinxed_you/th_Stroke_Material_v01_ch01-pg009.jpg[/img]

If it weren't for the gutter, my mind would be homeless.

Yea, I read it myself, Its Stroke Material.