I was found guilty without any witness only cops who got there after the matter is this legal?

ok to make this short i had a permit to carry a gun this guy pulls a gun out on my mom as i come out my house he shoots at me i shoot back he starts running away and shooting as he does he hits his brother in the head but he lives by the time the cops show up he gets rid of his gun now i never been in court and i was unemployed when this happened so i could not hire a lawyer and was appointed one so he tells me to waive my preliminary hearing i had no clue what that was so i agreed with him not knowing that it takes you straight to trial ok so at trial the commonwealth had no witness but as i said cops who showed up after everything happened so this what i was found guilty on (Aggravated ault) (Criminal Conspiracy Engaging - Murder) (Poss Instrument Of Crime W/Int) for defending my life and my family don't i have the right to face my accuser in court is there anything i can do i get sentenced June 1