You first need a proper test taking strategy, to ace any examination be it your Mock Test or IIT JEE Exam. The strategy should ensure you finish your strongest section in minimum amount of time attempting first, followed by given more time to other sections, and completing the paper in stipulated amount of time, as such you are confident of securing atleast 40% of the Total Score.
Besides test strategy, you also need proper strategy in selection of preparation Material for Self Study. Besides good books as well as NCERT, I would like to suggest you few of the crucial materials which helped me during my JEE Advanced Preparation
1. Arihant Chemistry Handbook
2. Allen Maths Handbook (PDF Available)
3. Resonance Rank Booster Package (PCM) (M&Adv)
4. MS Chauhan Organic Chemistry
5. DISHA Target JEE Advanced Book + Previous Years.
For more information and JEE Preparation Tips do follow the link below
So from what i could make out, is that you wish to make a JEE Mock test yourself for your self study? That doesnt make sense. However if you wish to try JEE Mock Test then there are book available for JEE Main Mock Test and JEE Main Past Year Question Papers so that you can practice them within 3 hr time.
Also, NTA provides this opportunity to try and mock test made from past year paper on THIS WEBSITE (https://nta.ac.in/quiz) .
If you have a further specific query please feel free to comment.
Best of Luck.