Why do T-BILLS appear so lucrative?

If I bought a T-bill with face value of 100/- for 97/-, that’s a return of about 3.09% in matter of 91 days! And, in one year, of 3.09*4=12%!!
Where am I wrong?

Correct me if I am wrong but I think those returns are annual as per z-connect

Yeah but isn’t 12% per annum somewhat on the higher side? When banks give 6% per annum