Sandbag Question

I’ve just constructed 2 100lbs sandbags. I filled little sandwich bags with sand, wrapped them in duct tape, put three of these bags in a larger baggie, and then tossed those into a duffel bag. The duffel bags is about 18" x 34" I think.

Here’s my question. The bags of sand probably only fill around 50% of the duffel bag. There’s a lot of extra space, so the duffel bag is very floppy. When I heave it up onto my shoulder, the front half hangs on my chest, and the back half hangs on my back, with nothing in the middle.

I know the bag is supposed to be an odd, hard-to-carry object, and this certainly is. But I was wondering if it would be better for me to fill up the rest of the duffel bag with newspaper or pillows or something, to make it more full. Or is it better to leave it as it is?

Anyone who built his own sandbag have an opinion?

I’d make it more full (I use sandbags all the time)