Hey Rohan,

Your JEE mains rank 31143 is sufficient to get admission in Thapar University, Patiala in Computer Science and Engineering even you don't have domicile quota i.e. you don't have completed your 12th from Punjab. 

So you are eligible to get admission in Thapar University for Computer Science and Engineering according to last year cutoff

Last year cutoff closed at 32471

Good luck, hope this helps