A white lie is small until you need three more to hold it up.

A small untruth is not a single object, it is the first piece of a structure. The moment somebody asks a follow-up you need a second statement consistent with the first, then a third to prop up the second, and now you are maintaining a building in your head during a normal conversation. What makes it expensive is not guilt but bookkeeping.

Catch it at the first one and correct it inside the same conversation, while it is still a slip and not a story. Say you got that wrong and give the real version. One awkward sentence now instead of six careful ones later.