No way are you a bad mother, you did something that generations of mums have done to try and comfort their child. As everyone has said the risk is miniscule, almost negligable - but a risk nevertheless. I remember being at a friends BBQ, she is a GP, i mentioned about the honey thing - she laughed at me, but then she went on to give my 8 month old a Dorrito and wondered why she nearly choked , she doesn't have any children of her own.
It is natural to worry with a new baby, it would be wrong if you didn't and you do sound like you are having a hard time with reflux and colic etc. This WILL settle down.
I think you should speak to your HV, excessive worrying can be a sign of PND, it might be worth you taking the Edingburgh test just to assess if you might be suffering a bit, you don't need that on top of a colicky baby.
I only knew about the honey thing because i read it in a book that the HV give you, it was a tiny little aside in the book, otherwise i would have been as as you were.
Be kind to yourself, you are a wonderful mum and deep down you know that - but everyone has "im a crap mum moments".
Have a chat with your HV to get some reassurance - do you belong to any baby groups? It might help to find a group of mums who have similar worries and challenges that a new baby brings.
You are doing a great job - be kind to yourself!