Having second thoughts for second child??

I have one daughter she will be 3 in February. She was a super easy baby. But she is a mommy's girl and I love her with all my heart. Lately, my husband and I have been talking about a second one. He's always wanted more I always said no one is enough. But I have been thinking about it. It's just do hard because I feel like I love her SO much that I can't even imagine loving another. I was the oldest out of two and definitely felt that my mother always cared more for my sister even though I was the "good kid" and I don't want to do that to her or another one. It's seriously a big fear of mine. But at the same time I don't want her to be an only child. Anyone else have these thoughts or feelings? What did you decide? what was the outcome? Are your child actually equally?