

CAD (cardboard aided design) is really powerful. You get to fail fast: figuring out things don’t work before more expensive manufacturing steps (such as laser cutting).
And using inkscape is fine, but even better if you print it out and stick it to cardboard.
In the US there is no notice period for firing in “at-will” states (which is all except Montana). It goes both directions though, there is no notice period when quitting. So chances are, if the OP is in the US, the boss was full of it.