My first thought here was check your hydrometer to make sure you are getting accurate readings.
1.008 is low! Pretty amazing honestly, mine puttered out in the .020's - however, I found mine to be WAY to sweet, as do most other brewers who brew the 120 clone for the first time by the book. Check out this topic:
This is where a good collection of home brewers including myself have all posted our experiences brewing the 120 while reading on about Scottland's experience, lots of good information in there and you may get an answer faster with the members subscribed to the topic. Personally I would feed it more sugar if you want to sweeten it up, if you used American Ale and a 099, it can't go much further past 21 and if you do, kudos! Beef up the dry hop accordingly.
Something to keep in mind, the general consensus of that topic and the brewers that have made the 120 is that it finishes too sweet, teens is a good place for that beer. Also, more hops all around for both the boil and dry hopping stages.
Good Luck! Cheers!