That looks like normal expansion. Gaping, unfortunately, starts with the tissue that seals off the openimg on the underside of the shell detiorating so initially it's impossible to determine from a clams normal opening and closing.
Looks good to me but I am far from an expert. Is this a newer addition? I only ask because the shell just looks awfully clean. Do you have a white new growth line on the shell? It is the first thing I look for on clams.
I'm envious of your photography skills. I can never seem to get decent images of my clams.