Told my stepmother her and dads baby would be posion now i feel bad?

Hey ok look im 15 . About 10 years ago my mom left my dad for someone else, at the time i didnt understand i was told by my dad 'my mom didnt love us anymore'.I hated the fact of how my dad was in pain for so long after it and was not himself ,after a few years we began having great fun,football games cards everything!!...................when i was ten then my Dad brought home a woman he liked ,when i saw a new woman coming in i thought pure danger,i loved a mans life with my dad and with her coming in i thought she would ruin it as she was a lot younger than my dad,I couldnt let her get in the way and ruin my bond with dad!!!.....i then began 'Battle' tryed to get dad to end it tryed to act sarcatic to get rid of her i did everything to make her hate us i tryed for two years but i could see dad like her and he said he made her happy,it crushed me.I then told my dad how i felt but all he said was he hasnt been so happy in years and he really loved her and blah blah blah!!............They got maried last year to my distaste and made a baby together, the baby is born now its 2 weeks old and its a girl,about a month ago i told my stepmother the baby she was expecting would be pure poison because its from her.The baby is born now and i feel bad for what i said,dad was mad too,but it really annoyed me because i wanted to go to football game dad promise last year he would take me its about 5 hours away in a city this team only play here once every year.he wouldnt take me incase she would go into labour and he wasnt there WHICH WAS STUPID ,because she wasnt due for another 2 weeks!,i got so mad i took all my anger out at my step mom and told her everything i felt about her.I just don't want a woman in the house since my mom to be honest!! but now i see her kid and i feel bad for calling it poison and shouting at my dads wife .how do i say sorrry,im not doing it for her, im doing it for dad mostly ?shes been ignoring me since i said all the mean things to her.