Oops! Got yer dimensions a bit off then.
Make the DXF 3 inches tall, 3/4 inch thick and include the rabbet. Then, with a Display Cube .76" wide, 3.01" long and 48" deep, apply the DXF. Back in Part Editor, select the contour and "Create Part Using Closed Contour."
All of this is, of course, assuming you only want the part for display purposes. If you want to machine the part on a CNC then you will have to use a Display Panel (from sheet stock) of the correct dimensions and create a tool from the DXF. The tool would then be used to profile the edge of the Display Panel.
One thing I noticed that might be where your problem came from. If you hover over the back (flat) side of the shape, it is actually two 24" lines. It looks like you took half the shape and mirrored it. When doing this I have found it is best to delete one of the straight lines and extend the other past the intersecting line and trim it.