I already know the answer
You have mixed up the death methods. Telling the lie will get you hung, as it's more painful - a slow torturous death; whereas being shot would presumably kill you in an instant. In any case, had you proposed the riddle accurately, the answer is:
"I will be hanged." You see, I can't be hung, because I'm not lying, but I can't be shot because being hung is for liars. Therefore, my statement is a contradiction, and thus sets me free.