I'm new to 3d printing. I recently designed my 1st part from scratch. Basically just a disc with a recess and a through hole. I used sketchup as I've been a woodworker for years and am familiar with it. I drew up the part and exported as a stl. Opened in cura and the part looked just as it did in sketchup however when I printed the part it printed as a solid disc no recess no hole. Any ideas what Ive done wrong?