Can an employer make it mandantory to sign a paper stating you have to cone in if they call you in on your day off?

Yes. Your employer can require you to work on a scheduled day off and fire you if you do not work that day. This is an employment-at-will state which means you can be fired for any reason and there is no liability for the employer unless there is an unlawful motive for the action taken against you. There are generally only two forms of unlawful motives: unlawful discrimination or unlawful retaliation. Discrimination in employment is unlawful if it is due to race, color, sex, national origin, religion, disability or age 40 or older. Retaliation in employment is unlawful if you engaged in one of a handful of "legally protected" activities and were fired for engaging in that activity. If either of these was the motive for the termination, then you may have a claim for unlawful termination.