At about 1 hr:20 min in the film, Jimmy & Terry are fighting outside the rear of Elliot's house. Jimmy eventually hits Terry three times with a shovel. The 3rd strike causes Terry to pass out & drop his gun which goes off accidentally when it hits the pavement and shoots the 'other Jimmy' in the shoulder. The next shot shows Terry still unconscious but holding the gun in his right hand.
When Angela gets shot, the bullet enters high on her left shoulder. This is a non-fatal wound. It's nowhere near any vital organs, and it would take hours, if not days, to bleed out, assuming it was left untreated to begin with.