Uhm... wtf?
I'm not so convinced by the physics engine...
In the first level, placing a + behind the projectile should be more than enough. The speed of the particle is not supposed to drop when it gets far from the source of the field: it's the strength that drops, and with it the acceleration. Another way to see it is to say that at first Coulomb potential energy is converted to kinetic energy, but when the projectile is far enough the potential becomes constant and so the kinetic energy.
Instead, the projectile slows down and slowly deviates towards the upper right corner: does it feel the field of the - charges up there? Maybe while not feeling the + charges?
Anyway, the trajectories are too weird for my taste, making easy levels much harder than necessary and hard levels too annoying.
I understand this was only a school project but please don't brag about using scary physics equations...
P.S. The major wtf goes to the comments, as always... I've read at least 5 reviewers referring to magnets, really sad...