Getting into a mathematics master's program from engineering?
"Force = Mass * Acceleration."

You appear to be worried about your inferior "mass." What you may not realize is that you have superior "acceleration" to compensate, probably bringing up your "force" level to at least average.

I entered a math-oriented PhD program with someone who had only one year of calculus, but whose "acceleration" you remind me of. Within a year, he equalized in "mass." Then his superior "acceleration" took him to the top of the class.

The same could happen to you, if you have the natural gifts and "bent" that you say you have. Your engineering gives you enough "background" to get in the game.