I hadn't thought of Forrest Gump, but you're right. I wish they'd done something else with the dorm room scene. It seemed out of place, and, I think, damages the movie. Everything else in the movie, such as the violation of Jenny by her father, was suggested subtley enough that an adult could understand it, but without the explcitness that dropped it downward.
The scene where he tells her, "I'm not a smart man, Jenny, but I know what love is", and then walks out onto the porch and puts his hands on his hips is brilliant.
I think I understood the dorm scene. Forrest had just "defended" Jenny and Jenny was testing Forrest to see if he could really be the sort of man she wanted but, of course, Forrest didn't understand the invitation. The point was to show that Forrest loved her like 10-year-old friends on the school bus rather than as someone to have sexual relations with. This convinced Jenny that Forrest was not the answer she was looking for.
While I've enjoyed many other films, this is one of my all-time favorites because it speaks at different levels on a wide variety of subjects (romance, war, faith, promises, how society deals with the handicapped, fate, politics). It gets that rare compliment from me - a movie I can watch several times and pick up new things from it each time. Most Hollywood fare is so shallow and stale that I can only stand to sit through them but once (and sometimes not even once). If more movies were like "Gump", the industry wouldn't be such a cesspool.