It's an incredibly hard thing to get over the feeling that you have to be, do and act a certain way in order to try and convince someone that you need the assistance that you clearly need. I think a lot of us have been there at one time or another. The feeling that someone else holds your life in the palm of their hand and you have to somehow prove yourself to them in order for them to let you live it.
What I would say, hon, is that people sometimes pick up on how you say things more than what you actually say. Your body language, the way you express yourself, and your demeanour can often be far more telling than what you're telling, if that makes sense. And, as Mariah alluded to, telling people what you think they want to hear is sometimes the worst approach to take because subconsciously you'll be looking out for clues from them that they're "buying it". And that's noticeable. It has to be about you, and how you really feel. If you're just honest about everything, and speak from the heart, with emotion borne of exactly how you feel, and why you need to do what you need to do, then that's also noticeable... and goes a lot further in stating your case to anyone listening.
The trouble is, it can be a vicious cycle. You're scared of saying the wrong thing, and that's injected into you trying hard to say and do the "right" thing which may have exactly the opposite effect and come across as you trying to be who you think you're expected to be rather than who you are. Even if they're the same thing.
Sweetie, I know this is very, very hard to do, but you have to try and think that there is no "wrong" thing to say. That you don't have to try and come up with reasons why you need the help you need. You already have that, and your post here makes it clearly apparent that you do need assistance to be yourself. That's you speaking with no pressure. And that's how you have to try and approach the situation. To just tell your story, from the heart, rather than trying to word the perfect story to tell.
*extra big hug*