No, it's not compulsory to take coaching for CPT exam if you have confidence to prepare it yourself and if you prepare with correct strategy.
I am suggesting some steps that you can follow for your preparation :

1.Thoroughly study syllabus of exam
2.Practice previous year question papers so that you can understand the type of questions asked in exams.
3.Make a proper strategy for your preparation.
4.Give more weightage to your weak subjects.
All the best