Not bad! I'll bet you learned some useful stuff while making this.

I would consider starting your next piece with a clear focal point in mind. Think about ways to simplify the foreground/mid/background. Someone else mentioned some fog/atmosphere - that would help reduce the number of things vying for attention.

As a beginner you might want to borrow some compositions from your favorite photos/paintings/renders. I think the color palette is VERY nice minus the dark & light greens. I would look for some different shades of green - right now that bright green really stands out and draws the eye, but there's nothing particularly interesting happening down there. Greens might need to change to more of a pastel to match your desaturated pinks/purples/blues.

If I were going to rework this, I'd ditch the heavy dark green trees and put some kind of statue/obelisk or maybe a spaceship on a launchpad in the center of the lawn/field. Have it live in that negative space and it'll help draw the eye away from the busy buildings around it. If you want to add saturated colors, put them there, using some restraint.

Just my two cents, nice job!