First no, you can't change Construct's absolute angles. In Construct RIGHT is always 0 degrees, DOWN is 90, LEFT is 180 and UP is 270. That's just how it was built and all other behaviors and functions reference this.
Secondly, lerp has nothing to do with Construct, it's a math function. And because of it's nature you never truly get to your destination since lerp is ALWAYS halving the distance, which is why there are so many decimal places. So you need to write code to compensate. i.e. when it gets to a certain point just set it to your destination. You will run into this problem in any language.
If you feel so strongly about C/C#/C++ I'm not sure why you are using Construct as it is all java based. I suggest you use Unity for C# or create your own custom engine in C++.