How to calculate the hybridization of ethane with H=½[V+M-C+A]?
The mistake that you have made is incorrect understanding of M. From what I remember, M was number of single bonds, which would be only with a monovalent atom, in the context you learnt tbe formula. This was taught in chemical bonding where only atoms are bonded to central atom. 
Ex- PCl5, PCl3  
You should modify this definition to get the answer  here. Any monovalent group (-CH3) should be there in M.