Hi Saunskruti,
Please don't do any of the yogic asanas in excess as a replacement to exercise.
Both run on different principles.While most of the exercise leads to burning of calories and strengthening of the used part, yogic asanas are more into the overall correction of the body system.
No doubt that Suryanamaskar is a whole body exercise but you should not do it in excess. You should have started with 3-5 Suryanamaskar increasing gradually upto 12, that also under expert supervision with all the necessary precautions.
Shavasana is a must after suryanamaskar.
Try doing a combination of asanas under proper guidance rather than doing merely for the exercise purpose.