Did I make a mistake in choosing civil engineering at DTU and leaving COE at Thapar University?

No, you did not make a mistake in choosing civil engineering at DTU. Here’s why.

Civil Engineering at DTU: 

• Choosing Civil at DTU is actually beneficial as you have a core branch. This means (Government+Private+PSU) jobs and a number of opportunities available in the government sector. Government companies hire civil engineers more. 
• Since you have opted for DTU you are in NCR with a lot of exposure to different aspects of engineering. If you clear GATE with a good rank you can easily get selected in a PSU. 

COE at Thapar University: 

• The COE or computer engineering branch is the same as or somewhat equivalent to computer science. 
• Opting for COE would be a great choice only if you’re interested in coding. A private university like Thapar University would be the way to go for you if you would want to pursue COE. 
• Opportunities in the Government sector would become limited as COE is not a core branch. Private companies are more likely to hire COE students than the government sectors.

It might be difficult for you to choose since both the branches are exceptionally good. It would be beneficial for you to pursue Civil Engineering at DTU if coding/programming does not excite you. 

DTU is a reputed college and civil engineering being a core branch will not disappoint. If you put in the required work, it will definitely be worth it. It’s not as easy as computer science.