its my fault?

O benim hatam mý?

 O benim hatam = It is my fault (a statement)

but Its my fault? with the question mark implies the question

Is it my fault? Which I think is something like:

O benim hatam mý ?

I would say either what you did "O benim hatam mý?" or, if you want to emphasize "my" (as in: Is it MY fault?) O benim mi hata?

I´m just learning too, so if that´s wrong somebody will hopefully correct it

Yo are right but "if you want to emphasize "my" (as in: Is it MY fault?) O benim mi hatam?"

 Ahh, yes, thank you so much. I wasn´t sure about that one.