There are many white varieties out there that can look very similar to yours. You need to provide more details. Does it bloom early or late? Are the stems sturdy? Are there any scent? How tall is it? It maybe peony Baroness Shroeder if your peony blooms late and is about 3 ft tall.

Thanks.

It blooms late (after Coral Charm), has a scent, and flower stems are about a yard long, sturdy.

Baroness Shroeder looks possible!