The side that is curved, when placed by itself (without bending or manipulating in any way), is not a polygon, making the shape not entirely made of polygons. A 3D figure must be made by only...
No. By definition a polyhedron has to have faces (flat surfaces), edges, and vertices. A sphere, hemisphere, and a cylinder are all solids but are not polyhedra.
The sides of a rectangle are not all equal so a rectangle is not a regular polygon. And, as a consequence, any 3-dimensional shape made from rectangles cannot be a regular polyhedron.