Is passing cute notes in college class, subtle or bold flirting?

[Municipal]

There is this sweet guy in my class. He definitely likes me, and I like him too. Our study load keeps us busy, and Im shy around him. This means we dont really communicate and spend time together. He asked for my phone number but I misplaced it a few days ago. He is a gentleman. He does things like hold the door, "ladies first", humors me, ask how was my day, wakes me up when I fall asleep, and other sweet things. The past few days have been stagnant. So to have a little fun and to get things rolling, I send him a note. It was a small square paper, that had a giant smiley face on it, which read "hi". He was surprised by it because I usually am quiet and aloof but I do smile at him. We kept passing notes and I think he enjoyed it. Buuuut tell me was that a little too bold or just right?