It seems that Geology is your subject of liking but due to certain compelling reasons and circumstances you landed in B.Tech. Anyway, it is not late and you can cover it by going for doing B.Sc. with Geology first and then doing M.Sc. (Geology). B.Sc. Geology is a 3 years course and you will be incurring these 3 years before you go for your dream post graduation degree in Geology. There are so many good institutes for B.Sc. Geology and if you get admission in them then that will be a good beginning so that you can easily get admission in M.Sc. Geology.
Another alternative is go for M.Tech. in Applied Geology for which B.Sc. Geology is not mandatory and B.E./B.Tech. people are eligible for admission in it. This M.Tech. Applied Geology course is for 2 years and admissions are based on the score of entrance exams like GATE, TANCET and also 10+2 scores. After M.Tech. in Applied Geology there is scope for the positions of Geographers, Oceanographers, Geologists, Meteorologists, Seismologist, Completions Technologist, Processing Geophysicist, Researchers etc in various organisations like Central Ground Water Board, the Geological Survey of India, Coal India, Oil & Natural Gas Corporation, Mineral Exploration Authority, Hindustan Zinc Ltd etc.
Knowledge is power.