I'm glad you liked the concept and atmosphere despite the issues! The corner of the window bug is a weird one that I still can't find anyway to fix. I've played around with various forms of stretching the viewport, etc but ultimately I'm not sure if it is something with the engine and how the web build works. I made another 3D game with the same engine and built for the same platform and it doesn't have the same issue despite me following the same exact process with it too, so really hard to pin down the issue. More strange is that minimizing and maximizing the window has worked on a couple of machines to solve that problem, and a big part of why I added the fullscreen button to the web build is to fix that issue.
For moving the ship forward, either left clicking on the mouse or W/Up arrow key should work to move forward. We made the game completely playable using just a traditional mouse but there are the keyboard options too. Turning is entirely off the mouse position or the right thumbstick of a controller if you have one plugged in. Not sure why it's drifting, we haven't been able to recreate that on our end with either a windows or a mac for the web version. My guess is it's reading some sort of mouse movement that isn't happening so I'll have to look into how I can prevent that.