D3100: Macro mode

I wanted to take some pictures of the serial numbers of my cameras(D3100 and Canon S95).

The S95 was able to take crispy clear images of my D3100 and 18-55 VR lens from a close distance.

Then, I put the Canon S95 upside down, turned the D3100 into "Macro scene mode" and tried taking the picture.

I am unable to focus on the Serial No of Canon S95 using Auto Focus or Manual Focus.

What could be the problem? Is it D3100 body limitations or 18-55mm VR f3.5 limitations?
Will screwing a 52mm Macro filter on the lens help?
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D3100, 18-55mm VR, Canon S95