I'm thinking of this movie plot... don't remember the name?

It's a late 90s or early 00s movie iirc (I could be completely wrong, though).

The movie starts with a girl borrowing/renting a dress to attend a party, but something spills on her so the dress gets WRECKED. She's freaking out because she doesn't know what to do, until some nerd offers to pay for the dress (it's a few thousand dollars; the money was going to go to a telescope otherwise) in exchange for a huge favor:

The girl has to pretend to be his girlfriend, but she's hot and he's not, so they embark on a massive change for the guy, from clothes, hair, interests etc, until it is revealed that he's quite the hunk--throughout the movie, the girl slowly starts falling in love with him as he becomes more and more attractive, but with his newly found looks and confidence, he begins to have eyes for other girls.

Their 'fake' relationship ends, the girl is torn up, but soon the boy realizes that he misses/loves her and in the end I'm pretty sure they get back together and it's a happy ending.

Does anyone else know this movie??