My LO was the same. I remember because i was annoyed the small 4oz bottles were condemed to the cupboard forever more and I shouldnt have got so many lol.
Its fine, I was worried too but the health visitors put me at ease. They said to me if he was overweight they would suggest things (dont know what, mabye hungry baby milk?) but they said let him drink upto 7OZ!! if thats what he wanted. I found by giving him what he wanted I had a very happy and content baby!! x