Water and gas don't mix so settling that it is going to do will happen in a few seconds after the shaking stops.
Debris is another matter. It can settle to the bottom and sit there until shaken, then take a long time to settle. But if that was the problem I would have expected the boat to start okay and then develope problems as you ran, not fail to start after sitting.
If you managed to flood it while attempting to start you should just leave the throttle open wide for a few minutes and try again.
If you have any reason to suspect the gas then definately check the fuel/water separator. If your separator is the type that will allow removal of the "bowl" without dumping the contents then remove it and inspect before you toss the contents. If there is water in it you should be able to clearly see it.
If you have to drain the filter before you remove it then try to catch the contents in a glass jar for inspection. Water will be sitting at the bottom. The gas should be all one color with no debris floating in it.