Sigh. Yes. The perspective of a woman who has dealt with countless come ons in every style imaginable.
Our OP already asked her out. She declined. Maybe she was truly busy maybe she wasn't. She didn't offer a counter either. She's on the fence at best.
Here's why the response suggested by
@Learning Curve sends the wrong message:
OP already asked the chick out. You can't undo that. In the invitation his interest is assumed/obvious. THAT is why the suggestion from Learning Curve comes off spiteful as
@JoyDivision1990 put it; but thurt as I put it. He's invited; she's declined. Facts. Now he suggests saying he is going to think about it too? That makes him look completely idiotic. What are we, 12?
The only self respecting type response is exactly what the OP did. Neutral/chill. Kudos to him.
I am emphasizing this because context matters in this scenario. My neutral response is context appropriate. Learning Curve's is not. Who cares about this girl. She's going on a trip with God knows who doing God knows what anyway. Leave things open with her and while she's away at the beach meet other women.
The debate of the finer points matters for the reader who might find himself in a similar scenario. A neutral comment displays an attitude of outcome independence.