Spray it again, Sam
Finishes in aerosol cans often clog the spray nozzle. This is especially true with polyurethane. Here's a simple solution for cleaning spray nozzles that allows you to use the entire can of finish.
Soak the clogged nozzle in a small jar of mineral spirits (or the proper solvent for the nozzle's finish) for at least an hour. Remove the nozzle and, while it's still wet with solvent, use a can of compressed air to clean out the passages. The extension tube on the can of air fits perfectly into the base of the nozzle to force the clog and excess solvent out. Wipe the nozzle with a clean cloth and attach it to the spray can. You can save the solvent in the jar for future use.