"I was always always a happy little girl
All the flashbacks come back to me in one big swirl"

there are two "always" when there should be only one.

"because I really dont like myself"

dont should be don't.

"What happen if I did go, no more me
You and everyone would be full of glee"

I think it would sound better if you put "would" after what.

"I really cant stand this
Even when I am dead, I didn't have my first kiss"

cant should be can't.
And in the second line, I would reread it, the last part doesn't make much sense to me.

"When I am gone, I left a left a letter"

^should be: "I left a letter".

"Even though I know your life is better
So is mine, I don't half to be full of pain
Because now I am in the arms of death and hes keeping me sane"

hes should be he's. Otherwise, I love that last part, good rhyming and very heartfelt. So my advice would to just go back and look over this poem, and make some changes. But other than that, this is a good poem that has good emotions. Keep writing, always and forever...