Yes, you can start writing your mock test if you have completed your 70% of syllabus.

Make sure you complete the topics which carries more weightage in the exam.

You should write mock test to analyze your preparation level and to know your strength and weakness.

Mock test are there to get you familiar with the exam pattern.

Work on your speed. Time management is very important for any exam.

It is recommended that you should learn from yuor mistakes and try not to repeat them.

You should solve 2 to 3 mock test daily for your practice.

You can also refer to previous year papers to understand the level of the exam and sometimes, you can get direct questions from that.

Al the best for your preparation and exam!!