Hi 

There are two kinds of registration involved in CA CPT exam- one being the CPT course registration, for which you had to register before June 20, 217, in order to become eligible for appearing in CA CPT exams, and other is CA CPT exam registration, which is the first step to filling application form and not an eligibility criteria. 

Assuming you are talking about CPT course registration, then I am sorry but you will not be able to appear for CPT examination any longer, if you didn't register for the CPT course before June 30, 2017. It is so because CPT course registration has been closed for new candidates, after the introduction of new scheme CA entry level exam, i.e. CA Foundation. 

Now, to appear for CA entry-level examination, you will need to register for the new scheme examination, i.e. CA Foundation and CA Foundation course. Like CA CPT, CA Foundation is also conducted twice a year, in May and November. You can find complete details about CA Foundation from the link given below. 

The exam application form for CA foundation for May session has ended now. Since you have appeared in Class 12 exams, you can register for CA Foundation course now, and can appear for CA Foundation (November session exam). Please remember, in order to become eligible for CA Foundation (November 2018 session) exam you should register for the course on or before June 30, 2018. 

Know the complete details about CA Foundation 2018. 

Hope it helps! All the best!