Delhi University (DU)

Cutoff for M.Sc in Nursing in Delhi University hasnt been released yet, you can check last years cutoff and prepare likewise

To an extent, you can obtain B.Sc in Life Sciences admission at various Lower South Campus University colleges which are affiliated to Delhi University. Since you have obtained a low 300/600 score in PCB during the CUET exams, it is therefore unfortunately impossible for you to be admitted into any North Campus College but there’s still an opportunity for making it through to South Campus colleges. Such include a list of the colleges one can think about Swami Shraddhanand, Shyam Lal, Aditi Mahavidyalaya, Satyawati Evening and Bhaskaracharya College. Feel free to ask any further information or questions.

640 out of 800 is a quite good score in CUET. You can get admission into various reputed institutes of Delhi University and other universities also. But according to rough estimates, it may be difficult for you to take admission in North campus if you belong to general category. Also, you have not mentioned the category, so it is difficult to give you the answer of your question. Although, you have a good score of almost 80%, which will definitely help you to get admission in reputed institutes without any problem. 

To get admission in B.Sc. Psychology course at DU then students are eligible to apply for these course if their graduation score is above 50% and after appearing for CUET entrance exam. This course is 3year duration. The top psychology colleges at DU are Daulat Ram College, Kamala Nehru College, Aryabhatta College, Zakir Husail Delhi College and many more.

You can use Shiksha college predictor-

https://www.shiksha.com/college-predictor

Any score above 450 is good to qualify for DU.

So you have chances.

Also you can try for other good universities like CURAJ, BHU, Luckhnow University, Aligarh University, etc.

It's very difficult to get DU on asked CUET score under the SC category. The CUET score above 650 can be safe for DU for the SC category.