Worried about being a mommy?

I am 8 months pregnant with my first child and I am worried about treating her like my stepmom treated me. I was raised by my stepmom and was treated like the typical disney stepchild. she was always short and has a bad temper. She would belittle me and yell at me all the time, no matter what i did. I see myself doing some of the same stuff to my 9 year old nephew. He has ADHD and it can get stressful when i babysit. I feel bad that i lose my temper with him but he also knows what ons to push and he pushes all of them. Please dont be judgemental, i really am worried that i am going to treat my daughter like my stepmom treated me and alienate her. I love her so much already, but i dont know what to expect once she is born. Any advice, please be nice!!