I finished the pin and when in object mode it looks pretty decent, but when I render it the pin turns into a large square. Did I mess up the geometry when I merged the mesh? When I applied merge by distance, I accepted the default distance and blender reported removing 20 doubles.
First off, press ~ (beside the number 1) and View Camera. Do you see the pin there? It may be that the pin is visible in the viewport but not seen by the camera when rendered.
In the Outliner, click the Filter icon and under “Restriction Toggles” enable the camera. This camera will show up to the right of objects in the Outliner. If the object has a camera with an X in it, it won’t be rendered, even if it is visible in the viewport (like my Pin Mesh object).