As mentioned, two things will prevent that in the future:
Uninterrupted, undistracted time on the handle;
Powder that fills the case at least half full (with the appropriate level of attentiveness of course);
The 550B is a great press and there is NO SUBSTITUTE for paying attention - you are engaging in an activity that can result in catastrophic failure if all isn't followed methodically.
With low levels of powder, the COAL isn't going to tell you anything relevant, nor would it be helpful to try pushing the bullet in as there is plenty of room inside the case, and every bullet should be able to seat deeper regardless whether it is properly charged or not (depending on crimp of course).
And a random weight check won't really help either, except to verify that the charge is proper and consistent, as it only takes one bad round.
NO DISTRACTIONS!