「彼氏と彼女の　三三九度に　坊やおなかで　高砂や」? Saw this " " on the TV show : < My dictionary says = "perform the ceremony of the three-times-three exchange of nuptial cups", but I still do not understand the second half & hence the whole thing.

is a ceremony performed at a wedding. is a Japanese comic story related to a wedding. means "their child in her womb."

So the sentence means "Their child in her womb tells a Japanese comic story at their wedding". That is about "shotgun wedding".