Hi,

The amount of milk you can express tells me nothing about the amount of milk your baby is getting.
The fact that she is growing and thriving, weeing and pooing tells us all we need to know - you two are doing great, and she is getting plenty of milk.
The amount you can express might tell me that you are "new" at pumping, it might tell me something about the equiptment you have or your technique of expressing. It might even tell me a little about how anxious you are.

40 mls is not bad going, really. You can freeze these amounts, or add them together to make a bigger bottle. 80-100 mls will be more than enough for a feed for her.