OP you did your best and gave them a good life, therefore you were a good mum. Don't listen to the people who berate your for your honesty. Many mothers probably feel similar, you can love your children and not love parenting them.
I don't have kids, never had the urge, and I'm glad I didn't give in to societal pressure. I also see how worn out and stressed my mother still is with us even though we are all grown ups - she takes on all our problems, and my brother gave her so much stress over the years it was ridiculous(think drugs, violence, police involvement) Then my sister got pregnant as a teenager and my parents had to support her, I was a bitch as a teenager, and then went travelling abroad in my 20's and they always worried about me.
Overall I think their dreams of a quiet, relaxing, affluent retirement were scuppered by our antics.
And now when my parents are elderly and getting ill, my brother doesn't even contact them anymore. I know my mum is heartbroken. You can put so much into your kids and they can still turn out to be selfish.
Plus, they don't just stop needing you at 18, I don't think its possible to switch off the caring mode, even when they are adults, it's a lifetime job.