On my warmer the element is bent in a circular shape, but when you purchase the element it comes as a flat element
Well then, I suggest that you get with whoever you purchased it from and have them replace it.
It all depends on the model that you have not supplied. And yes, some elements are supplied in the raw. But without the machine model I don't want to lead you in the wrong direction. There are serious tricks to making elements and they require some special tools that you sometimes have to make for the application. Poorly done will result in a short life.
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