Advice for a new step mom

Hey, so I am looking for advice here. My boyfriend and I have been together for almost a year now. We moved in right away together so we've been living together almost the same amount of time we have been dating. Things are great, we get along great and hes amazing and I love him so much. He has a beautiful 3 year old daughter and he shares custody of her with his ex (week on week off). His ex is totally crazy and treats him like shit but he does his best to keep things moving smoothly as that is what's best for his daughter. Hes been calling me the step mom to his daughter for about 6-8 months of our relationship now. I love his daughter, she is a sweetheart but I am really struggling and I dont know what to do because I feel like a total asshole. I have never been in a relationship before. My boyfriend is my first everything, first boyfriend, first sexual partner, first kiss, literally everything. So here is my issue, I want him all to myself. Of course I can't have that, and I know I cant have that. I knew he had a daughter when we started dating, I knew he had shared custody of her. But I still struggle a lot. I love that he is a dad and is an amazing dad, his daughter is so lucky. But I find myself struggling with the fact that I will never come first for him. When we are cuddling on the couch and watching a movie he will abandon me instantly to cuddle his daughter if she asks, he gets mad at me if I say I dont agree with something he does when parenting her which bothers me because he calls me her step mom, shouldnt I be able to voice my opinion? And I just hate myself for feeling jealous of a 3 year old. I keep catching myself wishing he hadn't have had a kid before he met me, and I know that is wrong. And I would never ever treat his daughter wrongly. She is a sweetheart and I do treat her like she is my own, but it breaks my heart sometimes knowing that I will never be the woman to give him his first child. Are there any other step moms on here who can help me? I want to be able to put this stupid jealousy behind me, my boyfriend doesnt notice it but I feel it and I dont like it. I am also a total control freak and do everything also, I get her dressed in the morning, I bathe her, brush her teeth, I've taught her the alphabet, I'm working on teaching her words so she can start reading when she goes to pre-school in September, I cook all of her meals and i even buy a lot of her clothes and new toys. I spend a lot of time bonding with her and she absolutely loves me. I am almost always the first person she asked for when she wakes up in the morning and she always calls my name when she need help with something. So us bonding is not an issue. She even calls me mom sometimes, which I have tried to correct because I feel like it's too soon for her to be wanting to call me that. I just dont know what to do. Does anyone have any tips for me? Has anyone gone through the same thing? Will it pass with time or is this something I am going to have to struggle with for a while?