How do I appraoch her after this?

So today I (19M) arrived a bit too early for my class and decided to go outside for a smoke. As I was walking down the hallway, I saw my crush (19F) with her friends. We made eye contact and I started wondering if I should say something. As we walked past each other, I suddenly heard her say “Hi,” but I just kept walking and didn’t say anything back.

Later, after our class ended, we were both heading outside. The door was about to close, and she held it open for me. This time I said “Thanks” but she didn’t say anything back.

Now I want to acknowledge that she greeted me and held the door open for me, but we don’t have classes again until Monday. I feel like bringing it up 4 days later would be weird.

How should I proceed?