In a stout, you may not get under 1.020 or so. There are many factors involved in attenuation- from the yeast strain used, the ingredients in the beer, the temperatures, the health of the yeast, etc.
If you post your recipe and process, we can see if that's a reasonable FG for you. I had several extract beers that would never get below 1.020 no matter what. I assume it was the extract I used, and the amount of non-fermentables I had.
In a stout, 1.020 may be perfectly acceptable. I'd wait another week or two, and check it again. If it's still the same, it would be safe to bottle.