E9X series tires are smaller than the F30 series. The rear on a staggered E90 is 255/35/18. On the F30 its 255/40/18. Thats a 4% diff in overall diameter. Fix the tire size and it wont look undertired like Maz said.
F25 X3 N20:
2010 B8 A4 2.0T quattro (current)/
2013 F25 X3 x28 N20 (babymobile)