During key match incidents, it is incredibly important to raise your concentration levels to avoid making errors. Most assessors can accept a technical error or a bad habit, but when a KMI is incorrectly done, you can rest assured that the report will not be kind.
In this case, you recognized the initial error in the KMI but failed to correct it. This is probably, for me, the bigger problem. If you had thought you had seen someone touch the ball and made the error then ok. If you didn't know the Law, then ok. If you had a lapse of focus and awarded the goal, then ok. But having been aware of your mistake before having restarted play and not correcting it is significantly less ok. Here, again, the fact that it is a KMI means that it is tremendously necessary to get it right, even where you might lose some standing with the players. In this case, it sounds like you were very lucky that the players were completely ignorant--but now they don't think they're ignorant and when the same thing happens again, any future referee will have an extremely hard time giving an IDFK the other way.