What chance have they now?

Some days...when I seem to fail the most or when I lose the control or patience I am reminded of the thought that has plagued me since my children were born. What chance have they now? As much as I wanted and begged God for children...why did he give them to me? I feel like the most unqualified person to be called "mommy" by these two people. I mean some can be good parents because they can scrape together some kind of attack plan from their own parents...I certainly don't have even that. Everyday we live together I feel like I am swimming up stream...I am desperately trying to keep one step ahead of the challenges of parenthood. I am learning everything for the first time. What does nurture look like? What does healthy discipline look like? Will my kids only remember the times I fail? Will they remember the times I lock myself in my room and cry because I got frustrated and raised my voice? Will they grow up to be afraid of me? What chance have they now? Wouldn't a better woman have been better suited for Eli and Madeline? How could I ever be the best they deserve? How?