It's all so confusing, I know because I am a first time mum too! My bub was a tiny bit under at birth and lost 12% of her birthweight so I was advised to wake her every three hours for feeds. She was in hibernation for the first 2 weeks so would just sleep, sleep and sleep (oh how fondly I look back on those days!!!).
She is gaining weight now and wakes of her own accord so I just follow her lead. She is 8 weeks old.