I have a cross beak chick that is about 6 weeks old. It started just like yours and within a week it was double what yours is and now much more. I have been worried and have been watching her every day. Even with the bad cross she is eating and drinking fine. This is the first cross beak I have had so I'm not sure what to expect, but I did read a post where someone kept one well into adulthood. I'm going to let her continue to grow as long as she can eat and drink.