This ball is foul... from your original post, I gather that you knew you made a mistake calling it too early.
I had one similar when I was just starting out:
R1 and R2, no outs. BR attempts a bunt down the first baseline. He lays it down (great attempt), and the ball is rolling up the line and is headed toward foul ground with F1, F2, and F3 huddled around it and coach screaming "Let it go foul, let it go foul!" For some reason, F1 lets it roll and quickly picks it up when it's on the line! I yelled, "FOUL!"
I immediately cursed my poor call under my breath! I must've sold it pretty well because no argument was made. To this day I don't know why I made that call!
I learned from that mistake, and I'm sure you'll learn from yours.