How to stop my Pointe shoes being so loose?

You could try using vamp elastic. Vamp elastic is a wide piece of elastic that you sew at the throat of your pointe shoe to keep your toes from "knuckling over". If you sew it tightly onto the shoe, it could help it to be tighter. Also, you should tighten the drawstring to be as tight as you want, then tie it in a double knot and cut it off to be a couple inches long, then you tuck it in. But usually, your shoes will become baggy when you go onto demi pointe.