jee aspirant. I am worried I am a dropper and I have not completed my syllabus yet and exam is in January. what should I do

Dear Sanjay, don't worry, losing hope is not a option. You still have more than 2 months and I can assure you if you study hard and prepare well you will be able to score well.
Since not much time is left you can analyze the exam pattern and Weightage of each chapter and start preparing according to that, as covering maximum syllabus with highest weightage should be the priority. Also chemistry is the most scoring among all the three subjects so try preparing more chemistry topics as it contains easy questions compared to other two. Try to attempt as many mock tests as possible, you will definitely get an idea about the questions. In JEE MAINS manytimes questions are more or less same.
So, don't worry start preparing now.
All the best
Hope this helps