I haven't used Quikrete, so I don't know, but wouldn't "mortar mix" mean it was for laying bricks? I thought it wouldn't have gravel in it for mortar. Before you buy a bag of the portland cement, do you think you could screen the mortar mix you already have out from the gravel? Maybe use an old colander? I would think you'd need to use a mask or something to cover your nose and mouth so you wouldn't breathe it.
'Or cover the colander with a cloth.
Maybe try a small leaf if you can? Don't know if that helps or not.
