Hey Divya, don't be afraid. Accept the nomination. At the time of uploading the documents to IRCC Portal just make sure u to upload ur baby's passport, birth certificate. Don't b panic the same has happened with me as well in past. Make sure to attach the mail which u hv sent to NOVA Scotia immigration officer for intimating about the change in your family composition. Rest the process will remain the same. They won't change the nomination certificate now. You have to inform the CIC now about the baby.
Congratulations.
Regards