I'm not sure of when the best time to give up is, and if not how to turn a girl around if she's getting distant/cold.

If a girl starts to say she's really busy/with her friends and can't hang out what's the best option. In regards to texts should I:
-Leave it alone for a couple days and "ping" her to see where she's at
-call her out
- completely ignore
- other

I was thinking about trying out this text:
"Hey so I met this cute mysterious (color of hair) girl last weekend and I wanted to get to know her. But she's always so busy... I need some advice"

Any tips?