Which is a better strategy?

I am in college and I got this number of the girl I am into.

I forgot to give her my number tho. What's next? If I call her or text her, she wouldn't know it's me.

Should I have given her my number too?

What do I do from here? She plays the piano and I mentioned that I used to play it but haven't played in years and wanted to pick it up again. She didn't express interest to show me though...is that a not-IOI?

Basic little thing you can do is when she gives you her number, just call her right away so she has yours too. (To be clear: The second you put it into your phone, you're standing in front of her, she doesn't pick up.)

Calling her while she doesn't have your number will only be a problem if she doesn't pick up when she doesn't know who it is. (Tends to happen with girls that go out a lot, big cities, etcetera.) If that's not the case it is no problem, no worries.

What to do from here? Well we know very little about your situation, so just set up a meet and continue gaming. "She didn't express interest to show me though...is that a not-IOI?" No, that's not a 'non-IOI' (IOD- Indicator of Disinterest). She could be too shy to set up a date herself, not confident in her own abilities, etcetera. Don't overthink, dangerous shit.

Good luck,
-ZeroValley

Text her

"Save my life, buy me a coffee.. This is ________ by the way"

Zero is right. Call her as you are standing there. Whether you make a comment about it is immaterial. This has three advantages:

1. She may text you later, a definite IOI
2. She will be more likely to actually pick up when you call
3. If you haven't introduced yet, a chance to share your name (for her to put in her phone). The intro-handshake is also a chance to make physical contact, in case you haven't before.