Love the concept!
Just a couple of things I would like to see in this.
1. Without knowing the context of the shirt "amusement parks," it's a bit difficult to to extrapolate that the short knight (SK) is being rejected for the siege. Or at least, it's not immediately apparent that is the intention. I would add maybe a long line of tall knights behind the catapult, or have it pass by the SK. Or even have a ride entrance gate with festive amusement designs!
2. I'm not sure if it's my computer, or just the template, but the artwork isn't very 'clean'. I think your lining could be better done and would really make this image more instantly memorable, this also applies to the detail in the wall.
I know this is a lot of work, but more effort and hard work will make entries like this a formidable entry.
Excellent start though! I enjoy entries like this instead of woodland creatures in funny poses...