Hello Teesha ,

Different B.Arch colleges have different guide lines for the marks required to get addmission. Generally for a decent college , 50% marks in 12th Science stream and a valid nata score is required. While some colleges also consider 50:50 ratio of 12th and Nata score. 

Considering your score , you might not be able to get into the top ranked colleges. You should apply for the new colleges , they generally consider this score , have good faculty but are low ranked. If you have a state board then you can easily get into these colleges of your state , they have some 50% reservation for state board students. 

Hope this information was useful. All the best.