scared about getting bc at planned parenthood

I'm trying to plan out a way to get birth control at Planned Parenthood and I'm terrified of it. I'm 16 and this will be the first time I've had to make an appointment on my own. My mom cannot know about this. I hate having to go behind her back, but I need birth control and I know she'll get mad or at the least turn it down if I ask for it. For the phone call, what do I say? Do I just ask for birth control? Also, it will be out of my own money, so I can't do or get anything really expensive. Is there anything that I should be expecting while I'm there? Can my boyfriend go with me? I'm going to need him to help me stay calm during this. How is the service there? Is it intimidating or is it more calm? Will be people who work there be really helpful or will they just give me it so I'll leave faster? Will they even give it to me since I'm so young? Sorry for so many questions...I'm just really nervous. I'm used to my mom being with me for doctor's appointments, but that isn't an option in this situation