Take what's left of your box of cereal, bring it back to the store and let them know about the recall. Have them replace that box of cereal.
Call your OB to reassure yourself, but also call the cereal company and let them know that you'd like more details. I see no reason to freak frick out. Stressing out over this is more harmful to the baby than anything else. That's so counterproductive, don't you think?
Think this through. The recalls don't say that it's actually in every box. It's a safety measure so that someone doesn't accidentally eat metal fragments and hold the company liable because t hey can't pinpoint which boxes actually have the metal... they just know which batch the fragments fell into.
Next, realize that you would likely know if you were eating metal... you'd feel it on your teeth and break a tooth.
Even if you did swallow metal chunks without realizing it, your body can't digest it. It would pass through you undigested in a bowel movement. Your doctor would probably not want to do any unnecessary tests to see if it's in your digestive tract because those tests would be more harmful to the baby than if you swallowed a piece of metal that's going to get passed through you anyway.
I would think that the higher risk is to breaking a tooth than choking or leeching to the baby. Because even if you managed to actually digest a piece of metal, your placenta and uterus and umbilical create quite an amazing system there to protect your baby from harmful toxins.