Navy quilted duvet cover set, queen size

I lost my navy quilted duvet cover set—queen size—with two pillowcases yesterday around 3pm. It's navy with a subtle quilted pattern and white piping along the edges; the fabric is a soft cotton blend and there's a slight fade from washing. I think I left it on a bench near the Peace Gardens by Pinstone Street in Sheffield city centre, possibly by the City Hall. One pillowcase has a tiny coffee stain near the corner and there's a small snag along the top seam. It was a gift from my grandmother, so I really need it back.