Your hours of work are a matter for agreement between you and your employer, and whether or not your boss can make you work on the weekend depends on what is in your employment agreement.
If your employment agreement includes undertaking additional work as reasonably required, then this may involve weekend work from time-to-time.
Depending on whether you are paid a wage or a salary you may be entitled to overtime for this.
If you are required to work weekends on a regular basis, then this should be reflected in your employment agreement. If your employer wants to change your agreed hours of work, they need your agreement.
Your employer must not require you to work hours which might put your health and safety at risk.