Whilst IggbyB is right, I agree with Dot in that you could make things so much worse by going down the legal route just yet. It seems to me that your ex, by not letting you out of her sight with the baby, has got serious issues re trust and keeping her baby close, right now her guard is up and will protect her 'cub' with the ferocity of a tigress. Not that I am saying that she has any reason not to trust you or that I think her actions are right, but your ex will be very fragile at the mo and with such a young baby, very sensitive.
Dot is right, stay in touch, dont push it and take it slowly, build up the trust again that may have been damaged in the split, for whatever reason. The more your partner sees that you are simply there to see your daughter and have no alterior motive, things may improve, as yet its very early days. However, if things dont improve, and get to the point where your access is being refused etc, then think about the legal route, but personally I think you should use that as a worst case scenario route.