ANSYS staff are not allowed to download attachments, please insert inline images of your model to help support your query. Also, have you performed a mesh convergence study and made sure that the mesh is fine enough? If yes, how much is the difference between both cases? There are bound to be some differences because of the assumptions made in 2D elements, but if the geometry is thin enough the mesh accurately captures the geometry, the difference shouldn't be very high. Also, if there are transverse or out of plane loads make sure to use at least 3 elements across the thickness of the model.