"Care was fantastic apart from one (quite large) mistake"

I had my daughter on in december at saint marys hospital, the care i recieved throughout my pregnancy was amazing and i couldnt have asked for more.My consultant was fantastic and my midwife was always available if i had any concerns. Due to my pregnancy being high risk i was seen very regularly and my daughter was born by emergancy c section due weighing 2lb 11oz.The care my daughter recieved in the NICU (Neonatal Intensive Care Unit) was of the highest standard and i am extremly greatful for all they did for her. My one concern is that at a few days old they discovered she had a PDA ( an open blood vessel in the heart) and was given medication to close it. After a few days on this medication i went to the NICU where a doctor told me there had been a mistake in her care. I was then told that they had wrote her weight wrong and due to this had given her the wrong dose of medication on several occassions. My daughter was given double the dose of medication she should have been for days. Surely in a ventilated premature baby a mistake like this should not be made? I do not understand why her medication was not double checked and why it was not picked up on as it was given frequently (not just a one off mistake). I was told that as far as they could tell it had done her no harm but it is still a very worrying thing to be told. I would like to add that all other aspects of mine and my daughters care were exemplary and could not be faulted.I would like to express my gratitude to everyone who looked after us but also my concern that this happened.