baby hasn't regained birth weight, do I let her sleep?

My baby is 2 weeks old tomorrow and is a few ounces away from regaining her birth weight. I usually wake her every 3 hours to feed but last night she ate at 2:30, didn't fall asleep until 3-3:30, and it's 7:41 right now and she's still sleeping. So it's been 5 hours without eating, I just really needed the sleep and so did she as she had been up all day and night. I can't help but feel bad though because I feel like she was supposed to eat. Also she is formula fed and gets 3 oz every time.