That's what I exactly got, it 'seems' to get slightly loose when I move around or smile. I had to push it back in to get it to 'feel' right.
I then used plastic food wrap and it seems to improve the seal.
I suggest try wrapping around some plastic wrap and see if it improves.
I think that i kinda a have the same thing with the right canal. Maybe the ear canal part is too short rather then to thin?