Hi Jacque,
She was staring at you through the corner of her eye in class and had her head sort of down when she held the door open for you.
These are indications that she is most likely shy.
A shy girl will often find it hard to be direct with how she feels with a guy she doesn’t know.
Telling you that she “kinda” has a boyfriend indicates that she didn’t want to let you down hard.
This is typical behavior of a shy girl. It can be hard for them to give a person a direct rejection.
Hence, they will flirt around it by using kinder words.
What she said had nothing to do with whether you came off as a “creep” or not.
This is how she would reject just about anyone who approached her that she wasn’t romantically interested in.