B.Sc Maths

Yes, it is possible to join B.Tech course after completing B.Sc through the lateral entry scheme which is offered by most of the Engineering colleges in India. The lateral entry is only given to candidates who have either completed diploma in Engineering or B.Sc course.
After completing any of these 2 courses, you can apply for admission in B.Tech through lateral entry scheme.

You will get admission in DU in B.Sc mathematics course if you have passed your 10+2 mathematics with 50% and 45% aggregate marks. You have scored 68%, so the chances of getting admission in DU for you are more.
All the best.

To get admission in Delhi University in B.Sc mathematics, you should clear your mathematics subject in your 10+2 with 50% and should score more than 40%.

There are two branches of B.Sc (Hons) maths seats distribution in BHU. Faculty of Science and MMV (Mahila Maha Vidyalaya). Faculty of science contain 460 seats which are common for both boys and girls. MMV (Mahila Maha Vidyalaya) contain 77 seats which is only for girls.