I have no idea what you are doing with her when you get together....I can tell you what I would respond to:

Wait until it's just the two of you (no TV or music or other people in the vicinity), turn to her and look her directly in the eyes and say "Did I blow it with you?". Don't smile or laugh or say it at the end of any kind of funny discussion. And, yes, looking into her eyes is very important.

It's direct and romantic. Don't say anything else. Just listen.

Good luck!