Am I stupid for this

My son is 4 months old and I’m following my pediatricians advice on when to start solids, how to, etc. everyone is saying I’m dumb for going by the pediatrician. My friend started her son on baby food at 2 months old and she has constantly told me she doesn’t listen to her pediatrician because she’s the mom and she can do what she wants. Also I supplement so I mix the formula first, then add to breastmilk. My MIL told me she was just pouring the formula straight into the breastmilk (fortifying but she didn’t know that’s what it’s called) so when I told her that my pediatrician told me to mix the formula with water first, she told me I was stupid for listening and that I need to stop going by my doctors suggestions. :(