OK I have imported the stl file as supplied into Preform and it does what you have identified.
I then imported it into Sketchup and the containing cube you have drawn is 3175mm x 3175mm x 4191mm tall so the proportions are way too big for the volume of the printer. I deleted the containing frame you added and then exported to stl. The file imported into preform as shown below.
Before we go any further there were some issues with the file import other than size. The file is not watertight so you need to look at that before you print.
I am not an expert with 3D software by a long way but is looks like your stl file in some way is getting rendered way too big from your original drawing, but I am no expert!