The fermentation temp, except for extremes, which is not the case here, won't effect FG. That being said controlling fermentation temp is very important and should be pursued.
If you want help trouble shooting the abv/fg issue you could post your recipe and procedure.
here are a few things to consider:
1. The final gravity in a recipe or brewing software is always an estimate. If you are fairly close and the beer doesn't taste overly sweet your good. Ex: 1.012 estimated fg; 1.015 actual FG and beer tastes OK, no problem. 1.012 est FG and 1.020 actual fg and beer tastes sweet= problem.
2. Too much specialty grains (crystal, carmel, etc) can result in a higher fg
3. Extract doesn't attenuate as well as properly mashed all grain wort.
4.If you are doing all grain mash temp effects attenuation