Is it okay to not want to call my stepfather dad?
What are your thoughts about why you don't want to call your stepfather dad?
Because I don't feel that he is my father.
Some step parents have to earn the fact they should be called mom or dad. Be more liberal with him and show him you already love him like a dad, which will make him happier to act more like one. You wouldn't want to refer to him as just "that guy who is my step dad" all the time, it will be too challenging for you both to get along in the future.
What do you propose I do? What if I tell you to shut up, who are you to tell me how I should feel?
I'm merely suggesting an answer to your question. Give your stepdad a chance and see if you two are able to bond over time. If he doesn't earn the title of "dad" in your eyes, then you can always refer to him by his first name.