Don't be too hard on yourself. A lot of B/C calls are so razor close. Sounds like you did just fine and since B2 was a secondary defender, that was your call.
But yes, reffing the defense is the key to getting the B/C correct. Also, a good habit for the lead on a drive is to back out from close-down to wide-angle. It's tougher to make the right B/C charge when it's right on top of you. You wouldn't have had to open up because you would have been watching the whole thing at a 45-degree angle.
No Hail Mary's necessary.
Z