You are NOT a bad mother!! We always go there as moms, and it's not going to help you to make yourself feel guilty over and over. Believe me, I know how hard this is for you. I am a mother of two and both have been in day care full time since they were 3 months old. It was hardest with my first because she was the first experience for everything. It has been easier getting my second there and myself ready for work in one piece, but I do miss her more during the day, probably because I now know how quickly the baby phase passes. My experience has been that it's never easy, whether you work part-time or full-time, to drop your kids off at day care. But what I try to do is focus on the positives - I can tell you from my first daughter's short little life so far that day care definitely helps them socialize better, talk earlier and with better syntax and vocabulary, and just generally enriches their lives! I can't believe all the little songs my oldest knows, and she knows all her numbers from 1-10, the alphabet, etc., and she's only 2 1/2! She has a ton of friends and a ton of interests. Also, you having a job and keeping your own sense of self and adulthood is SO important for your self-confidence. My co-workers are like a little family to me and I cherish that. It's just a different feeling of satisfaction that you get.
Believe me, we have had many mornings here where I've felt teary letting them go or guilty if one doesn't seem up for it, but you get through the day and spend quality time at the end of it. Keep your head up - we working moms are a special bunch and we need to stick together! It does make you a stronger person, trust me. Good luck and let us know how it goes in the future.