Hobgoblin Help

I brewed Orfy's Hob and fermented with S-04 (see thread https://www.homebrewtalk.com/showthread.php?t=37684). The OG was 1.056. I aerated it well and it fermented vigorously with a blow-off tube. It's been in the primary for 3 weeks now and my plan was just to primary, then bottle. However, the FG is 1.021! I checked it 2 days ago and it was 1.021. I stirred up the yeast and checked it today and it is still 1.021. That's an attenuation of only 61%. I know S-04 has a lower attenuation than Notty, but c'mon! It tastes very good (great recipe, Orf) and is still carbonated more than I would expect.

What should I do?... Add more yeast (not convenient and would take nearly a week to get)?... Let it sit in the primary for another week to be safe (for a total of 4 weeks)?... or just bottle as is? The ABV would be 4.6%, which isn't bad. Thanks!

I'd say 1021 is too high. What temperature is it?
How does the wort taste?

I'd be tempted to repitch but never having done it I don't know if it would effect the flavour?

I was very impressed with the taste, especially for 1.021. I never would have guessed the gravity to be that high by the taste. (Although, my palate is a little off due to getting over a cold). I double checked my hydrometer with water and it is accurate. It has been kept at exactly 70 degrees since fermentation began.

I made this 3 weeks ago, somehow got 1.064 OG, ended at 1.020, figured it's done, it's been cold crashing for a few days now, will keg tomorrow, last sample tasted GREAT! A little sweet perhaps, but great!