Should I retake the math portion in September??

I took the ACT one time in the September of 2019 and got a 35 composite with a breakdown of 36 E / 33 M / 36 R / 36 S. I know this is a really good score, but I am a bit concerned about math since I will be applying as a math major to elite colleges. Will the 33 hurt me? Should I take it again? Or does it not even matter?

No. At this point, it doesn’t really matter. It would be different if your composite score were lower, but the difference between a 35 and a 36 won’t matter in comparison to other parts of your application.