this same thing happened to me, im an emcce too, and when i would watch my performance tapes back, i was letdown.
it felt like i was killing shit on stage, but that wasnt the case.
you just gotta learn to let go and not give a shit about what the people in the audiance are thinking. perform like you do in your living-room when you finish writting something. the more energy you give out, the more the crowd will.
it takes time to get comfertable on stage. ive probably performed 30 or 40 times
(some poetry slams, some hip-hop shows) its still not completely natural, but its better. leave everything on stage man. its funner that way anyway.
.peace.
also, when you first walk onto stage, talk to the audiance for a second, joke around before you start performing, this helps break the ice for me.