The lowering springs put you in STX. I am not sure what the aero kit is, but it may bump you all the way to Street Mod. It’s the down side of SCCA classing, that an aftermarket wing moves someone all the way to Street Mod. If it is a factory option then you are fine in STX.
Looking at pictures of it, assuming it only has a very small wing if any, and I am guessing that you are a new autocrosses. I don’t think anybody would have a problem at the local level with you running STX. It may not be, by the book legal for STX, but we need some common sense where we put new people at the local level, and I don’t see the aero kit giving you anything but added weight.
Run STX at local events until someone says something. I doubt anybody will care.
This goes for a car that’s way under prepped for the class with a new driver. A car that’s prepped to the limits of the class rules, I would expect to follow all of the rules.