What does the ale yeast say the fermentation range is? If the gravity kept getting lower with each test it want done. Fermentation will slow considerably when you are at the lower range of the temp.
As far as bottle bombs, you won't really know till you open it. If it was in the fermenter for 3 weeks it should have settled well. Look in the bottles see how much sediment is there. If there is just a little you might be ok. Of there a fair amount, it might be prudent to open it outside or in the sink.