Roberta,
It sounds like the type of wrap I was sent home with when I had my tumor/hernia/hysterectomy surgery several months ago.
Is it basically one huge elastic band the width of your torso with a bunch of Velcro type fastener stuff on both ends that you wrap around your belly and secure with the Velcro? (Yes, they do come in multiple sizes. Sounds like the hospital was going the cheap route and only stocking one size.)
If so, have them send you a few of the "too small" ones and use two of them together by crafting one long one with the two smaller ones. It will work the same.
And, even after the doctor gives the go ahead to not use it anymore, there will be times when your torso and back muscles will be so sore that the only relief is from the extra support you get from that gusset. I wore mine on occasion long after I didn't officially need to do so.
Mine looked something like this (my body did not):