Okay I have a couple things for you to think about with this. One, here is a link that has helped me with measuring for scratch building a bunch. The link should start on the battlefleet gothic section, if it does not just scroll down to it. If you'll notice a cruiser for an imperial fleet is 95MM in length. I'm not sure what type of ship this one your making is, I'm assuming a cruiser or a battleship, lets say cruiser. So you'll want to be around the 90mm mark.

http://www.star-ranger.com/Scale.htm#BFGFor the second part i measured your previous pictures of this ship on my computer screen to get a general idea of how big you want it. This is what i came up with, 18cm long, 4.9cm wide, 2.1cm thick. Now assuming this is a cruiser size ship i would just cut the first number in half making it 9cm( or 90mm) in length. That in turn gives me my workable number to divide the other numbers by. I got, 90mm long, 24.5mm wide, 10.5mm thick, If we just used your numbers of 3cm wide 1.5cm tall and 10cm long, the ship would be bloated and out of proportion of what you where shooting for.

I do believe in the program you have you can shrink one side down to the length you want while in turn shrinking the rest of the ship to the same proportions.

Anyway just some food for thought in here, the added details you have done look fantastic, keep it up. This is scratch buildable at this detail if you want to try a hand at it.

Blind-