I used to try to rush the carbonation process by shaking etc. I ended up having to change my gas lines all the time because some beer would always make it up the lines. The quick disconnects also get contaminated and have to be taken apart and cleaned. What I'm getting at, is that you could shake it some more to make it more carbonated but that method ends up causing more problems. What I do now is set at 30 psi and let it go for 3-5 days depending on how carbonated I want it. The patience always pays off. If your carb level isn't right, just crank the gas back up to 30 and check it every 24 hours or so until it's where you want it. Another thing to remember is that if the beer isn't cold the CO2 will not dissolve in the liquid. So if you turned up the pressure and shook the keg while the beer was still at fermentation temperature, it would not have carbed.