A couple things, but big ones.
1. Extend the overall length and barrel length, unless you're purposely going for a very heavy sub-compact pistol.
If you're not, extend your barrel length to at least 100 mm (~4"), if not 112 or 120 mm (~4.5" to 5"). Your overall length should extend accordingly.
2. Increase that maximum range! Even with a 3.5" barrel, max range should be 75 m. Get it out to 5" and your effective goes up to 65 m, with an effective of about 120 m.