One of the guys I used to spar with would firmly tape a heavier weight to the top of his bag at home.

I wouldn't do this myself, but it works.

You can try filling it with something heavier. I don't know what material you have inside it so I can't give you examples of what you can put in, but look for something dense.

I'd just get another bag to be honest. Either way, bags are meant to train technique; this is possible even if the bag doesn't weigh extremely heavy. I'd only recommend you increase the weight of your bag if it goes flying everywhere with just a light jab.