I shouldn't imagine you've caused any serious damage. I've had nausea and stomach pain after reintroducing cooked food post-fast- it's one of the reasons I now eat a raw diet. The pain lasted 1-2 days on one occasion, and around 4 days on another, after eating a cooked meal on the first day of refeeding.
It doesn't sound like you ate too much 'problem food' in one go, so it should clear up soon. (As a side note, I've wondered if it's the salt, especially cheap low-grade table salt in food which pains one's freshly detoxed stomach lining so.)
Maybe consider seeing a doctor if it persists for more than four or five days, but I'd think that unlikely.