Cute, doesn't need much change to pass.
Mostly small things.
Show a mission carrying 35t to orbit, with successful landing after.
Some things with recommended fixes:
I noticed when I was flying it that it wasn't balanced. I know this can be tricky with small shuttles due to the short moment arms involved.
On the way up:
It tries to spin left if the RCS is off, and starts to successfully spin left out of control as the fuel levels go down. One way you can fix that is by adding a kolibri to the left of the frontier engine, that way you won't need RCS to fly straight.
On the way down:
It tries to tilt the engines into the re-entry flames and burn itself up. You can avoid this without using RCS by splitting your nose tank from the rest of the other tanks. This way, you can balance during re-entry just by having more fuel in the front instead of the back. Planes and submarines do this to stay stable, look up "trim tanks".
You only have 4 RCS, which is acceptable for a shuttle this big. But consider, do you need the 2 RCS on the body? Can you get rid of them and just have 2 RCS in the cargo door?
Parachutes... You have about 25 of them! You don't need so many if you're landing using the engines. See if you can still do it with 5 parachutes.
This makes your shuttle lighter.
Your cargo door has over 9t of fuel. I recommend moving most of that to the the separate nose tank I mentioned earlier, this will be more useful for balancing and you only need like 1t for a little bit of RCS maneuvering when you release the cargo.
Finally, a cosmetic change... Would this look better?