Your cervix has assisted you getting pregnant and carried your baby to term. Its doing its job and sounds like its in perfect working order. As the other's have said really they can only comment on the opening which should be small when you hadn't had a pregnancy at that time before. Timing also affects the opening of the cervix so if you had the tube in at a non fertile time of the month regardless of if you have had a baby in the past or not it would appear even smaller. Best of luck with your impending arrival.