No harm done! You can use the fuel you have.

The only difference between 4-stroke and 2-stroke fuels I know of (and that doesn't apply to all blends) is that the oil content of 4 stroke fuel is a little bit lower than for 2-stroke fuels.
Any average size glow engine will run well on fuel with 20% oil. Fuels containing only castor oil as the lubricant may however cause excessive carbon build-up on the exhaust valve of 4-stroke engines.

/Red B.