I have no idea what Nettle Beer is, and I think you may have meant "1.070" for your SG, or was that in degrees plato? It could have gone further if you let it sit for a while. How long did you let it go?
But, I think as far as keeping your beer cool (where are you?) you could try a basement (if you have one). At least a cooler part of your house might help.
If that's not available, try an evaporative cooling system in which you submerge your fermenter in ten inches of water (use a cheap plastic tub of some sort) and put an old t-shirt/rag/sweater/whatever over the fermenter. The t-shirt/rag/sweater/whatever will wick up water and evaporate and help to cool your fermenter. You can also add a fan pointed at the set up to increase cooling ability. This won't work as well in a humid climate, but it sure is a start.