NSTs, Twins, IU

Bella • I'm Bella! 20 years old, recently married, pregnant with twins! I'm also an aromatherapist. Psalm 139:13
I just had my first NST today at 31 weeks. I'm pregnant with twins, and the doctor said their heart rates look great but I have an irritated uterus (IU) and I believe that means my uterus is contracting irregularly? So they suggested I limit strenuous activity like long walks. How serious is an IU and what could this lead to? I should've asked my doctor when I had the chance. My whole pregnancy has been great and free of any complications, so I'm really bummed that this could put me at high risk while I'm in my final stages of pregnancy 😔 That and I'm not one to sit around and don't want to be on bed rest. Any of you ladies have a perspective on my situation or have been in the same boat?