Three months into RP, still newbie. (18)

I was at a very important project today that lasted all day long. Gf texted at 12PM asking at what time will I be done. I told her that we should be done by 5PM, but did no give a set time ("I'm 100% positive that by 5 we will be done"). She asked if I wanted us to go out if I wasn't tired. I said yes.

The program got very fucked up, and I had to do the cleaning until 9PM. (No text no call from 12PM). I was like ok I'll let her miss me (RP lesson) because I did that yesterday (same project) and I had nice results. But when I called her now she acted somewhat upset/lowkey annoyed/lowkey disappointed that I did not call her or didn't tell her that the program got delayed so that "she would know to go out with someone else". Short answers, not much spark compared to when I called her yesterday when she was so happy to hear from me after a long day of planning and working.