Hey , 

Im afraid but the registration for 26/04/2019 applications are closed for the current academic year 2019-20. If you have any college of interest, then you can approach them through mail or their other exams through which you can get in. But the registrations for GujCET is currently closed and Im afraid but as far as I know , you can't appear for this year's Exam. You are eligible to apply for next academic year though. 
Try getting to the desired colleges by going through the official website or any other national exams like JEE if you have attempted. OR If you have any specific college, then you can try with thier management Quota if it is provided. 
For further Information on gujCET you can refer : https://dqxeclau.top/exams/gujcet 
OR 
Try contacting them through their helpline number -18002335500. Even though they tell the same thing. If you have taken Exams like JEE mains, then there may be possiblity for you to appear for your desired college.  

Hope it helps, Good Luck.