Maybe the OP should just wait a day or two after his wife is done with her boyfriend to let her vagina sort of return to its pre-sex-with-monstrous-penis size. If that doesn't work, maybe she should see a plastic surgeon and consider having her virginity mechanically restored.
Otherwise, I'd say you're up the creek without a paddle... a big, wide creek, and a tiny, non-existent paddle. Wait - is that possible? Is it possible for something that doesn't exist to be tiny?