One part MC is good too, just not as flexible as the two part stuff. You will do fine with it as long as you keep your EC/ppm sorted. When you mix it, do your best to make sure the dry ingredients are well mixed, and you are better off making a batch of stock rather than only a small amount of ready to use stuff. Using a larger quantity of the dry mix reduces the chance that the ratios in the mix could be altered by the way the stuff sorts in the bag. Also, you are best off transferring the entire bag into an air tight jar that can keep it bone dry while being stored.
Good luck with it, I hope it all works well for you.