As long as you had fun, got some building experience under your belt it's growth and enjoyment. Is it perfect, no, you know that, that wasn't your goal.
A couple of simple pointers for you that won't cost a dime next time.
As mentioned, composition is a key element in a diorama, where are things placed, how are things placed, do they make sense.
If you put a slight angle on your diorama lines, so things are 90 degress, or all straight gives a bit more visual interest.
When you place things ask yourself "how did this get here? did the crew move it, drive it, push it, bomb it, drop it??" Then you ask "does that make sense?" Adjust accordingly.
Keep having fun.