1. Take it back to the store that sold it to you and let them mess with it.

2. Examine the angle of the derailleur on the seat tube. Sometimes just making sure that it's parallel will give you enough space so that it will shift inward just the little bit more that you need.

3. As a last resort you can install a 2mm spacer behind the drive side bottom bracket cup but I doubt that will be necessary once the derailleur is properly adjusted.