First of all, gratz on getting D2
What you been through is nothing new. A girl's investment in you will fluctuate. It could've been there was a lot on her mind and it wasn't you. If she was like that from the beginning of the date, then she probably had a bad day or much on her mind, hoping time with you will remedy it.
I've been through the same thing. Good convo but the girl seem to have much on her mind. Doesn't mean she likes you any less.
When a girl is like this, not the right moment to go for a kiss. To even get to that point, you need to put her in the moment with some mad skillz, escalate her properly with a series of Kino for compliance testing. Read her body language and IOIs.
Many guys kiss the wrong moment and get refused. If her mind is not there nor the attraction, this will happen. Also not all girls will be that easy to kiss. Some girls are conservative and some more liberal with kissing. Gauge accordinly.
Just plow through and set up D3. Don't even bring up about the miss kiss in the future. And definitely don't apologize for what you've done!