How to determine exact lagna

[roshankamath]

Dear members
Dob: 02 sept 1991, 03:05am( not accurate), Mangalore Karnataka.
Here is a horoscope of a girl. The birth time is not accurate. Would the time be 3.15 the lagna would be cancer instead of gemini. How to decide the exact lagna in such case.
Girl is very stubborn.
From a very good family. Father is a pandith n astrologer.
3 siblings.
Girl has a few broken relationships n not married yet.

Can anyone show some light on this.
Thanks

Regards.