Jason,
It looked like there is a 58 mm close-up
lens for $130.00. The only thing missing is the specs regarding the minimum focusing distance.
For using your existing lens/camera... in Macro mode Canon indicates that you need a minimum distance of from 3.9" to 1'6". Are you shooting with a tripod? That could be the issue.
When shooting in a macro mode the slightest bit of movement can make you out of focus. Even though you are shooting top down, some tripods are dynamic enough (configurable) to shoot top down.
I have a Manfrotto tripod I could let you try out. Let me know.
Bottom line....I am not certain that the camera is the issue.