B.Tech

Yes you can surely, based on your 12th-grade marks and because you already did mech, you are eligible and you will get admission easily, career-wise also in comparison to both civil engineering has a better scope, not that mech doesn't but comparatively civil is better. Actually to state it more clearly:
Mechanical engineers on average earn more than a civil engineer by $10 per year! However, the top 10% of civil engineers are paid more compared to the top 10% of mechanical engineers. So you have to work hard irrespective of whatever you choose, obviously, there is competition everywhere. However, in general, both streams are evergreen. More often than not, it is a matter of personal preference. If you get overwhelmed by the structures and construction, civil engineering is the one for you. If you are intrigued by the machine designs, their mechanics and dynamics, go for mechanical engineering. LASTLY, 1 FINAL PIECE OF ADVICE, IRRESPECTIVE OF WHATEVER YOU DO, CHOOSE SOMETHING THAT YOU ARE VERY PASSIONATE ABOUT AND WITH FULL ZEAL, HOPE THIS HELPS! WISH YOU LUCK FOR YOUR FUTURE ENDEAVORS!