Should I be concerned if I accidently ate expired food in the first trimester?

Yes. Well, yes and no. Obviously, we recommend avoiding eating anything expired due to the risk of contamination, but if you ate this more than two days ago and did not get sick then, your risk of food poisoning is almost zero now. Specific foods may have other risks.
Biggest risk was to. You, most likely with stomach upset. If you're ok now, then your baby should be as well. As always, please check with your doctor if you have concerns.