D.H.
It sounds like your baby is doing just fine! I wouldn't think of her like a 6 month old due to her size/weight. She'll need to eat more often more like you have been doing.
I wouldn't worry about asking the ped about how much she should be eating. She'll eat until she doesn't want anymore. For a baby just starting out, just give her a few spoonfuls, if the baby seems unsure.
I don't start a baby out with processed carbs anymore (cereals). The best first food (imho) is avacado. It's a good fat and good for their brain and body. I'm always a veggie person first too, but I wouldn't worry about that right now either.
Usually when a baby starts eating, they eat a few spoonfuls or 1/2 jar and you just give it to them a couple of times a day for starters. Eventually, you get to 3 times a day, but your baby just began, so it's more of a 'let's see if this sits with her well' kind of thing right now. You are basically making sure she can handle each food well.
You are doing great. Good luck!