Failure of a mom?

I feel like a failure of a mommy. My daughter is literally measuring on the small side 2.1 percent to be exact as of today (34w6d). They have me coming in every week for nst and dopplers. Everything is coming back good but it's still making me feel like a failure. Like I am doing something wrong. Mind you my fiancé and I were both tiny babies 6.9 oz and 6.5 I believe.