Am I really mean/senseless/heartless?

I had promised to go to my sister's house next week to spend time with her since she's having a baby in about 2 weeks........... but then they called me from work and asked me if I could work next week and I said yes....... then I emailed her and asked her if that's ok ..........and she got mad at me saying that "you have no desire to spend time with me so why would you offer to come to my house in the first place, you keep breaking my heart" ..........

is what I did that bad?

I feel really bad now :(