At the same time I myself am not worried about any mathematical issues when coding and so far I also never ran into problems with that. But in any case, I assume you're right in that it will be helpful to show that I can work with 3D.

If you got a decent grade in linear algebra, you'll do fine with 3D graphics programming.

The math and physics background you have already should serve you for a lifetime in game development. You just need to get those coding skills up to par.

I hope so :D
I'm actually in the process now to go through my hundreds of files to try and improve the quality. I always shied away from smart pointers because I thought they'd be complicated. Turns out I was very wrong...

I disagree with Kylotan about modding not counting as not relevant. It does count, my friend managed to impress his potential employer by modding pac-man into their RTS game.

I think you get bonus points for modding a game made by the company you're interviewing at. :)

Anyway, I didn't mean to imply that mods aren't looked on positively, but in my experience companies are looking for C++ foremost and anything else is just a bonus. Lua alone won't get you a job unless that job is "Lua Programmer".

Gameplay programmers often end up doing similar work to modders, using scripting languages.

I've never seen that in the wild - usually if there's a scripting language, we've had designers using it. Though I'm sure there are exceptions, especially where the engine is pretty solid and most of the game can be done in script (e.g. earlier versions of Unreal).