Raft Inflation Guide
It is easy to tell if you have enough air in the raft's air chamber tubes. Just push on the tube with your thumb and pump until the pump is hard to work. This will be close to ideal capacity.
When rowing you'll want enough air in the air chambers so that the tubes do not bend at the oar lock position. Cold water and cold air temperatures cause air to contract so if the air tubes soften, pull over and add air.
Conversely, air expands when it gets hot and a common caution for all inflatable rafts is to let some air out of your boat on hot days. I usually pull my Water Strider over into a shady spot if I am parking for a long period of time. If necessary, let some air out of each chamber on very hot days. You can always pump more air back in as needed to maintain optimal air pressure.