Good. The meeting being mandatory helps you. If the meeting was mandatory you must be paid for it.
Now, this might be splitting hairs, but the law is often about splitting hairs. The law does not prohibit the employer from making changes to your time card, but it does require the employer to pay you for all time worked, including a mandatory meeting. So what I would do is wait until you get your paycheck. If you are paid for the meeting, no harm no foul. If you are not, then you (and any other employee who does not get paid for the mandatory time) file a complaint with your state DOL.
http://www.llr.state.sc.us/Labor/wages/pdf/wcl-3.pdf
One caveat. SC does not accept claims for overtime. So if these two hours end up being overtime, you would instead file with the Federal DOL.