Hello

Don't worry there are many ways to get your user id ...

First check your sms from the cet on the date of registration, as they send sms after your registration. In that you can get your user id ..

Secondly if you not found the sms go to the registered email id  there you can find a mail from cet that also contains your user id..

If not than go to the official government portal of cet from where you have register. Go to the login there you can find a option , FORGOT USERID '...

go to that section, they will ask you some question .answer it and then you can recover you account...

Feel free to ask

Good Luck...