will my fuel go off

[amoret]

Oh bother, I just got home and realised that I forgot to close the air vent on the fuel cap of the portable fuel tank. Which is back with boat, about 2 hours drive away. It contains fresh 2 stroke fuel and I wasn't planning to go back for 5 weeks.
Will the fuel go off, bad, stale in that time? There's about 10 or 11 litres. May be just put the fuel in the car and start again? Nothing worse than launching boat at busy ramp and finding outboard doesn't start.
Would be useful to know however.
Many thanks in advance.

[RaymondR]

The fuel will be OK but you might lose some through evaporation and if there are significant temperature differences a small amount of water might collect in the tank.