[Rachel]

Did the SS have a chance to make a play(get to the ball)? Then its interference.
The coach did the right thing in coming out in a professional manner and asking you to speak with your partner. You could have said that "coach, it is my call and that's what I have". What you did was proper, speak to your partner and you can still say "coach, it is my call and that's what I have".
Umpires that work together are better umpires. In that situation you are in C and may not have the same angle on the hit ball as the PU does. It is not a sign of weakness to go with your partners judgement it is a sign of teamwork to get the call right.