That would indicate that pin 7 (discharge) isn’t working. When the output goes low again (and the LED goes off) pin 7 should go to ground and discharge C3 to prepare for the next cycle. For some reason that isn’t happening. It may be worth putting your scope on pin 6/7 and see if the waveform there looks like the diagram in the tutorial (I suspect C3 is staying charged from the symptoms) . I’ll see if I can find a 555 around here somewhere to experiment with.
Peter