TIFU by talking about a quiet new girl behind her back

This happened a few hours ago.

I was hanging out after school with a female acquaintance (let's call her sophie) and this girl from my year level walks past (let's call her quiet girl). Sophie said hi to quiet girl, and quiet girl said hi back shyly as she walked past. I observed this quietly, and while quiet girl was walking away, I turned to sophie and said "she's so weird". I'm not sure whether it was to teach me a lesson or what, but sophie yells out "Quiet Girl! throwaway123991509 just called you weird!". I looked away out of shame so I didn't see a reaction, but I'm pretty sure quiet girl heard it. I didn't even have any bad intentions, I was just tired after a long day of school and said something that came out bad, I actually feel bad for quiet girl and think she's kinda pretty :/

I currently feel like a huge asshole, because quiet girl always seems to look upset and she doesn't have many friends, but I don't have the balls to go up and talk to her (I'm a guy btw). If you somehow read this quiet girl, I'm sorry.