I'm a girl.... At least I usually am, but I've always had what I guess you could call 'penis envy?' I've kinda wanted to be on the other side of the gender spectrum? But I've usually felt happy where I am... A girl in pants and skirts and dresses. But now I'm wondering if there's a name for "mostly girl partly boy" idk I just always get this huge crash after my piriod where I feel like a man not a woman. I hate my chest, my curves betray me, I want something more between my legs, something of my own flesh. can someone provide some clarity please?

It's called GID (Gender Identity Disorder)
It happens
Not much to do except take things slowly and sort out your feelings, really

You're wondering if there's a term for what you're feeling? I know of two that would work.
Demigirl: Identifying as a girl, but not completely.
Bigender: Identifying as two genders. Can switch between them or be mix of both.
I can relate to you. I'm bigender and sometimes I absolutely hate being born female. I want to be flat chested and I plan on having surgery done later for that. I use he/him pronouns and go by two different names. Some days I'll dress feminine and others I'll dress masculine. I don't want a penis however as genitalia in general disgust me. But I definitely see where you're coming from. There are days that I long to have been born male. Even though my face can pass as male or female, my body is too feminine and I hate it. All of those feelings ssuck, I know. But having some call me by my male name and sometimes dressing masculine really helps with the dysphoria.
I would suggest that you have some close friends refer to you with a male name sometimes if you'd like. You can also get a binder to flatten your chest. But make sure it's a safe binder! I recommend gc2b binders. Also, for the penis part, I have heard about packers that give you a bulge, but I don't know much about them. I hope this could help you and I wish you luck!

Just to add a gender to >>3's list c:

There's also genderfluid, which is when you "shift" between genders. It's not always something as definite as "today I'm a girl" and "today I'm a boy," but it definitely can be. For other people, it's a vague, fluid move across a spectrum. (That's how I experience it.)

I know gender is difficult, and I wish you the very best. xx