Where did you get that pen stand? I am in Portland, OR and cannot fine one anywhere or online. Please help.
To answer your question, I suspect your problem is perspective. That is the angle of the camera sensor, I used to say film plane, to the object you are photographing.
Envision a tall building, if you shoot a photograph from the base of the building the top appears smaller than the bottom. The same is true if you shoot from top down.
Try getting the lens parallel (I don't know how to spell) to the pen cap and see what happens. Also, preview your picture while moving the camera around, you can see the different effects that occur.
You could actually fix this in Photoshop, but as an accomplished pro taught me, get the best picture you can into the camera and then fine tune the end product.
If you have a digital SLR, look into a grid focusing screen, this will allow you to check alignments while shooting. I believe some Nikon digital SLRs have this feature built in to the camera and you must switch it on from a menu.
This is a common problem in product photography, that is why many pros are still using view cameras and tilt and shift lenses that can change the lens angle to the film and product without moving the camera.
FWIW