BANG! An explosion of color and vivid light blossomed above. The irritated, sweaty crowd slowly rotated in the direction I had already turned. Our eyes locked on the streetlamp-illuminated sky as we anxiously held our breath. I began to wonder if the splash of color was a mere hallucination. Finally! Another sky flower lived and died. I sighed, and the defenseless group of teenagers I had spent my summer with sighed right alongside me. Relief washed over us; we turned and smiled to all the fellow faces we could find in the night. Disarmed by our childhoods, we stood and gazed with awe. The Fourth of July fireworks show had at last begun.

in this case, if im doing a junior la high school mla essay, should BANG be “Bang!” or can it stay they cool way it is? since its an onomatopoeia ?