I don't have the latest LL rule books, but most everywhere else, you have a Foul Ball.
You can understand why...Player's, particularly the batter/runner(s), hears the umpire yell "Foul", so they give up and start to return. Then the Defense makes a successful play on them. Not really fair to the Offense. It works the same in reverse.
If you call a batted ball "Foul", stick with it. Eat it. Do whatever you have to do, but don't change it.
Unless...You receive additional information from your partner that the ball was not foul, resulting in a Home Run. That is the ONLY foul call we change, because it had no effect on the outcome based on the players reaction to your foul call.
And next time, wait for the ball to SETTLE in foul territory, or come in contact with something that is not part of the field.
My son has the same problem with calling foul balls too soon. A late foul call hurts nothing. But an early foul call...Well, you know.