hi,

see majority of the school takes admission in 11th class, to appear in 12th board exam you have to complete the 2 years 11th and 12th and must fill the registration form as well as all the necessary information. you have to attend the practical classes as well. however since you have studied 11th class and have one year gap, you may contact with school authority to apply for 12th only. if this not possible and you want to save your year gap, it would be best choice to apply for nios, national institute of open schooling , you may take five subjects including one language paper and attempt 12th board exam from nios  board. nios certificates  is accepted by all institute in india for higher education.