Can someone answer my question?

Alexis • Expecting our sweet baby boy in April.💙 I thank God for giving me such a wonderful opportunity!
Okay. So I went to the OB today.. and she measured my fundal height, well i can normally feel my uterus pretty well when I'm having a Braxton hicks, and the top of my uterus was nowhere near where she said it was.... Is it just a certain part of your uterus that gets hard during a Braxton Hicks? Or could she be off?