solar system - Why can't I see Mars clearly?

Much like Jeremy has answered, Mars will appear just larger than a point, you will be able to discern a disk, however with minimal detail. For an overview of the disk you will see, I two versions of a virtual telescope in Wolfram Mathemtica; one with an orange disk and another using models of the planets. Anyway, using the orange disk variant, I input the CPC1100 details and the resulting view will match my output.

The field of view using a 40mm eyepiece without a barlow results in a 0.74degree apparent field of view, this equates to 2664 arcseconds. For reference Mars right now has an apparent diameter of 4.5 arcseconds, in your field of view that is .0017% of the apparent field of view (as represented by the orange disk).

eg. 40mm eyepiece @70x magnification w/no barlow

You telescope has a maximum useful magnification of 560x (2x telescope aperture) however it is airy disk limited to 481.2x. This means that a star will only appear 'point like' up to 481.2x magnification, above that the disk becomes increasingly blurrier to a point where you can no longer discern a point it appears as a cloud.

As a point of reference to the size of Mars using different equipment;

40mm eyepiece @210x magnification w/3x barlow

10mm eyepiece @280x magnification w/no barlow

17mm eyepiece @494x magnification w/3x barlow

On another note apart from what you 'should see', is what you can see. Aperture plays the ONLY role in telescope design which defines your clarity. The primary mirror diameter is a light bucket, a larger mirror is a higher image resolution (more discernible features/clearer image). Magnification also plays a role in clarity, each time you increase the magnification by 2x, you reduce the brightness by 4x; increase by 3x, you reduce brightness by 9x. So brightness is directly proportional to magnification. The highest possible brightness you can achieve, is your lowest possible magnification. How aperture works by collecting more light; allows a brighter image for a larger telescope than a smaller one at the same magnification, which is why so many people get 'aperture fever' and think big is best (for clarity yes). Your focal length is the determining factor for image size, meaning a 20inch telescope won't see an object larger than a 5inch at the same focal length.

You are correct in saying that both Mars and Sirius appear brighter with the naked eye than your lowest magnification; referring above, if your pupil diameter is 7mm, then the object appears at a factor of hundreds of times dimmer through your telescope.

I can provide material to calculate your own virtual telescope, it's parameters and viewing expectations if you are an avid user of Mathematica. Hope this has cleared up some information for you.