Sounds like you've got a very vigorous kit! This is totally normal. If you're growing oysters, lion's mane, pioppino, or chestnut you can ignore the mushrooms that may be fruiting inside your bag. If they're easily accessible you can break them off and compost them, so you can start fresh.
If you're growing shiitake, pinch off and compost any of the premature pins when you remove the bag.