[matsemann]

I assume you're trying to find the half-point by making a circle with center in each end of the line, with radius spanning to the other end. Which is too big for the game area.

However, what you need is to equal circles from each end point, no matter the size as long as they overlap. So the solution here is to make a smaller circle on one point, and using the compass make a "copy" of that circle with the same radius at the other point.