I have 3 months to submit my PhD thesis. What should be my strategy be like? I am going to write a manuscript based thesis. It will be having 4 manuscripts as chapters 3,4,5,6. 
Chapters 1 and 2 will be introduction and literature review. While 7 will be on conclusions. Now, I still have 50% work left for chapter 6, which I will complete withinn two weeks max. And will write the chapter as I go about doing the simulations to get the results.

My question is, I have to submit my thesis by June end. Extension is not an option. I am freaking out about deadline approaching so fast.

So, what should be my strategy be to complete the thesis on time? I know this is a vague question. But any advice would be most helpful!!
Make an output schedule that will let you finish.  By "output" I mean completed material, e.g. a page a day.  For each day, work at least as long as necessary to stay with the schedule.  

If you can do that, you'll finish on time.