Are you sure your bed stops heating? Curling of the corners may happen even with the bed still hot. If your bed rally would stop heating because of a technical issue, the printer would stop with a thermal runaway warning. So either your bad is warm but you still have warping (solutions would be a larger brim, or something like this), or your GCode sets bed temperature to 0 - in this case, watch your slicer settings - most slicers have an initial bed temperature (first layer) and then a follow-up-rest-of-the-print temperature. This may in your case be set to 0.
That’s a “known issue” - several solutions here in the forum - here is mine: Magnetic print sheet fixation - #10 by Hauke