Question: Gauge covariant derivative of a scalar field (D_mu Phi) (D^mu Phi)

I would like to apply my self-defined gauge covariant derivative (7) to the scalar field (9) in the form Dagger(D_mu Phi) (D^mu Phi) (13). But when I do this, my result does not look right. It seems that Maple does not treat my covariant derivative as a differential operator (or I did not tell Maple how to interpret it correctly). Also, my result (16) should not contain any matrices, after all I am calculating the scalar product of two vectors.

Can someone help me to determine the scalar product (D_mu Phi) (D^mu Phi) correctly? 

Could my error perhaps be due to the dimensions of my Pauli matrices? They are 2x2 and not 4x4.

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