Yes. Change back.

There is no need to move up to Step 2 unless you have a very hungry baby. Step 2 formula is casein based which is harder to digest so fills them up for longer. Step 1 is whey based and easier to digest. Step 2 is optional, not essential. You will not be adversely affecting her growth or nutrient intake in any way.

My MCHN always said that if your baby is happy on Step 1, don't change, and would recommend waiting to try Step 2 until 8 months of age when solids was more established.