You do not automatically forfeit your guarantee if OTHERS are late and are not sent home as well. Have your steward check time records, if that is the case. You can file for 3 if others were not sent home while punching late.
One of the tricks last year was Thanksgiving and Christmas, the Division Manager went around to every new-hire part-timer and told them they did not get time and a half for working the holiday and they had to go home! This was because volume was below the projections and he wanted them out! Some did leave unknowingly, but not enough. Very typical of the deception that goes on.
If there was anything I had a question about, I'd always ask to have a sit-down with a steward. If the manager or sup changed their tune pre-meeting and said "okay, well, this time I'll take care of you, we don't need to get <stewards name> involved", you knew it was a lie. (it happened often until I sat down and read the contract 1000 times)
Other than knowing the contract inside and out, this is probably the best way to do what's right.