You should be able to get some very clear and sharp shots with the 100mm L macro - and some very close ones:
a bare macro lens with no extension tubes or any other adjustments to the lens save focusing.
If you can't get a clear shot at regular macro distances then adding extension tubes, or any other method of magnification gain is going to just present more difficulty whilst your still trying to master the basics.
First up if you've a few shots it would be handly to have a look at them - along side info such as:
1) settings used - aperture, ISO, shutterspeed (rightclicking on a photo file on your computer - going to properties and then details in the properties window should show the shooting settings. Most editing software will also have a menu option to show this data (called EXIF data).
2) lighting - were you using any, what was it like? Flash, sun, spotlights, reflectors etc...
3) Weather - was it still or windy - sunny or cloudy?
4) Your overall method of approach to taking the photo - just a general idea of how you've approached taking the photo, combining all the above points to give us an idea of how you're shooting and how you're going about things.