I can think of a couple more things. If your fuel is burning up prematurely, you're either not putting enough in or you're burning it too fast.
With water in the bowl, you can burn at excessive rate and just boil the water faster without really getting the smoker hotter. Depending on wind conditions and how tightly sealed your WSM is, you should expect to have your bottom vents no more than half open. Before I added a seal to the bottom joint on mine, I had to close bottom vents on windy days to maintain desired temperature. My top vent always remains open.
Also be aware that the temperature measured near the center of the top will register low early in the smoke when the meat is still coming up to temperature. I use a Maverick remote reading thermometer mounted to the edge of the top grate and it can read as much as 50° hotter than the center of the dome. Later in the smoke the temps will tend to converge.
I usually use water for all smokes save fowl, but leaving the water out as others have suggested will help demonstrate excessive burn rates if that is the issue. This is good to test with fowl where low 'n slow is not as beneficial.
Regarding fuel, lump will tend to burn hotter and faster than briquettes. You might have a go with briquettes or a mix of briquettes and lump until you hone your skills.
Lastly, the meat picks up most - if not all - of the smoke flavor early in the smoke. If you run out of fuel before your meat is finished, you can move it to an oven and complete your work there. It will taste every bit as good as if you finished it on the smoker.
Make no mistake - cooking on charcoal is a skill and you will get better at it as you continue to practice and learn. And the more you practice, the more great meals you will prepare.
