You are not eligible for exercising the option for selection of old pay scale or new pay scale. Because it is for those who were drawing pay in pre-revised scale before 01.01.2006. See rule 5 of ROPA,2009. and Explanation-II
“Explanation-II: The aforesaid option shall not be admissible to any employee appointed to a post on or after the 1st January 2006 whether for first time or by subsequent appointment by fresh selection and he shall be allowed pay only in the revised pay structure.”
Annexure-III is the pay fixation statement and NOT the option form. Annexure-III is always filled up by the office and NOT by employee. You have no role here. DI has signed your pay fixation statement made in Annexure-III. Your pay will always be fixed with effect from the date of appointment after 01.01.2006. A new Annexure-III will be filled by school and forwarded to DI for new fixation in PG scale with effect from date of appointment.