Undo gradient fill

[chexnix]

   I had this border of arch leaf patterns on a design I was doing, and was messing with the fill. When I clicked the gradient on accident, the arch become this ugly blocky mess and it won't undo. No matter what i set the fill to, it retains that ugliness, and without reverting this I have to start all over...Any ways to fix this?

[Monika Gause]

Please show the object with the appearance panel and layers panel

[Ton Frederiks]

A screendump would have helped, but when I see the words "ugly blocky mess" i suspect the GPU preview.

Check View > Preview on CPU.