GCM Create M tables and R
The polynomial f would be 0xe1, no?

it is $e1 \mathbin \|0^{120}$ i.e. 0xe1000000000000000000000000000000

What would be the value of the element P, if it corresponds to the polynomial α?

it is 2 reversed i.e. 0x40000000000000000000000000000000