We used an open milk for a pesach recipe, a milk that had been used when having a chametz meal. Does that make the cake we baked to be chametz?

ב"ה Shalom, The fact the milk was open during the Chametz meal, does not automatically mean that Chametz fell into it. But even if it had fallen into the milk, at the time it fell it was not yet forbidden and it became annulled before Chametz prohibition time. In addition, the fact that this potential crumb fell into milk which is a liquid, it cannot later make the milk Chametz once Pessach begins. Therefore, if a crumb had fallen it does not make the cake Chametz since the crumb would have been annulled before Pessach. Mo'adim Le'simcha