Welcome to this foum.
As per Rule (6) of G.O. No. 198-SE dated 06.05.2003, your pay will be fixed in the scale of pay of Headmaster of a High School as per normal rules after excluding the additional increment which you were drawing as Headmaster of Junior High School.
I could not find the G.O. No. 961-F(P) dated 07.02.2011. Can you provide me this G.O.?