How do you quit spanking?

I'm not looking for the pros and cons of spanking; I've already done the research for myself. The problem is, I feel like I started off with the wrong choice and now am having a hard time breaking the habit. I've actually been working on it for a while, but a recent sickness has left me with zero patience and a great deal of moodiness and *I know* it's not fair to hold that against my kid, but, I backslid.

I was abused as a child, and I always sort of rationalized myself that at least I wasn't doing what my dad did, so I wasn't causing harm. But I know that's not true. My anger and shitty childhood are NOT her fault, just like her behavioral issues aren't exactly her fault either (she's 4). How do I stop and minimize the harm I've done?