because of this kind of low riding distance, engine and components are not warming upto the optimum temperature hence low mileage.
try to upshift at ~2.8k rpm, and accelerate slowly.
And what castrol oil you are using?? Try using any 10w30 grade oil if you'll be riding only 3-4 kms.
What was the mileage when you brought the bike?
Check if brakes are binding.
Dont tune/de-tune carb unless your bike crosses 7-8k kms in odo.
Given the condition you ride in, you should get ~35kmpl at least.

thnkx @Honda CBF for your reply.
I drive to and fro Station which is just 2km away to pick my Dad.
I dont known what castrol it is local mechanic advice me to put as he assured me that there is no need to change oil for next 1500km.
Carb tuning was done 4 to 5 time because of low FE. You are right I was getting 35 kmpl and not more than that. But that is too low and it should increase on highway but it was not.

well 2 km to and from riding is bound to give low mileage. But highway mileage should be more unless you rip it through out.
Try changing your fuel station..
Check tyre pressure every week & keep recommended pressure, never less..
Btw, what your mechanic & svc people says about the issue?

For some days I have used Dazzler only in the colony, mostly in 1, 2 and 3 gears with many speed-brakers. I got a mileage between 43-45 kmpl. When I used to ride to office with 50% traffic and 50% highway riding, I used to get 50-54 kmpl. On highways sometimes I rode at 60-70 kmph and I got 55 kmpl.

Riding in heavy traffic with pillion just for 2-3 kms everyday would give less FE, as said by Honda_CBF. But 21 kmpl is unbelievable. I don't think tuning is the culprit. There are lot many things that affect the FE. Low tire pressures, excessive use of clutch, shifting at wrong rpms, cheating when you fill petrol, and also wrong calculation methods.

I suggest you to get a 1 liter bottle and fill it with petrol. When the bike is going to fall in reserve, take your bike on a road with less traffic. When the bike hits the reserve, set the trip to zero, and fill the tank with 1 liter petrol. Ride till the bike hits the reserve again and check the trip meter. While riding, see that you shift the gears at 4-4.5 rpm. If you get mileage anywhere between 47-52 kmpl, there is nothing wrong with your bike. You need to look at your riding habits, fill petrol at a quality fuel station, maintain proper air pressure, shift gears at proper rpms. Also, I suggest you to use Honda 10w30 oil, which is certified by Honda and is a lot better than Castrol. The new 10w30 oil suits your riding habits and gives 3-4% more mileage than regular oils.

did you get your issue Fixed? my unicorn engine is giving some sound, i am planing to give harsha tomorrow

Planning to give my Unicorn to Harsha tommorow as there is some engine sound issue. i hope it get fixed