B/C sitch...what should I have done?

[KJUmp]

BHSJV I'm trail table side. Team A has ball in their FC, in the corner opposite table. Ball gets loose, and heads into BC with a team A player chasing it.
I have no idea who was last to touch in FC...(my scr**up), A touches ball in BC and wait a second to see if player reaction/body language would maybe let the play call itself. At this point I'm in front of B's bench he's loudly saying "backcourt." Team A player gets me off the hook by simply picking up the ball once he touched it, I whistle BC trying to give the impression with the slow whistle that I knew it was BC all along.
Major pooch on my part. Put it behind me and concentrated on the rest of the game, which was a close hard fought game, and actually had a pretty good game.... but I've been kicking myself since about the BC.

So my 2nd yr. newbie questions are:
1) What did I do wrong or have done better a the trail when ball went down into the corner?
2) When you're trail and DO NOT have definite knowledge of who was "last to touch"....no call and play on taking the heat for a blown call? I mean it's not like you can go to P for help, the ball is alive.

FWIW...as my second season will be coming to an end in a few weeks, I feel that BC calls overall are one of my weakest areas. I don't feel I'm much better at last to touch/first to touch recognition in the heat of the game...esp. at a higher (JV) level than I was last season.
I feel i've improved a lot in many area vs. last year.....but this is not one of them.