[Always *]

As Nicole said, you should give her time to cool down and talk to her.
There is only so much you can do to get her to realize it really meant nothing though, but it would be best if you explain why you were thinking about her and that it really meant nothing, and the LAST nothing it could possibly have meant was that you were cheating.
Once you give her time to cool off, and then you explain your side, that's really all you can do. She'll either forgive you or she won't