I have applied for three exam centres for neet but in the admit card i have got other exam centres other than what i have applied ????

If you carefully go through the information brochure that has been provided by CBSE, it is clearly mentioned that if the centres that you've mentioned in your registration form do not have the adequate amount to capacity to permit you to write your exam there, you'll be alloted a centre elsewhere.
This is probably why you've been alloted a centre out of your preference list.

In the brochure it was previously mentioned that tge allotment of the centres is based on various factors and may not obey the preference. You may contactvthe authorities to ask for help as centre was alloted without the choice you have given.