It's only been fermenting a few days. Leave it be - fermentation often takes 1-2 weeks.
It's often hard to tell whether it's still fermenting or not. No harm will come to leaving it to ferment for longer. I am guilty of worrying unnecessarily early about fermentation and bottling too early when the gravity is too high and on reflection it was obviously still fermenting - it went into the bottles like pond water and was hugely overcarbed.
If it truly is a stuck fermentation, then rousing the yeast can apparently help (though I've never had it do so) - try to swirl the fermenter without taking the lid off in case you introduce too much oxygen and spoil it. Raising the temperature can also help, but in a current heatwave I assume it's already quite warm.
If the cause of the low attenuation residual unfermentable sugars, then I dispute that it makes cloyingly sweet beer. I have had quite a few beers that (for whatever reason) have finished up at around 1.020 (from ~1.045-1.050 OG), and none of them tasted sweet. (Also see
Brulosophy experiments on the same topic). As I understand it, the reason for this is as follows:
- Mashing at a high temperature means it's predominantly the alpha-amylase that's active
- Alpha amylase produces higher quantities of long-chain sugars (Dextrins, Maltotriose etc) when compared to the maltose produced
- The yeast ferments away the maltose, but not the dextrins/maltotriose
- Maltotriose only tastes 30% as sweet as sucrose
- Dextrins don't taste very sweet
- Neither does maltodextrin
- So the only unfermented sugars left in the beer don't taste particularly sweet.
This has certainly been my experience, but your taste may be different (espeacially for those people who love to hate Brulosophy
)