I thought the most reliable way to know fermentation is done is to take 3 straight SG readings a day apart, if they are the same, it's done. With that advice it doesn't matter how incorrect your hydrometer is. 1.010 3 days in a row is just the same as 1.018 three days in a row as far as doneness...
There are a few websites and apps where you can type in your batch size and all of the fermentables, they will tell you what the SG was. Since it was all extract and sugar, you don't have to worry about mash efficiency, so if there is a setting for that, set it to 100%. Just Google recipe...
When I did my first batch, I forgot to close the valve on the bottom of my bottling bucket. I poured the priming solution first, but when I racked the beer from the fermenter to the bottling bucket, I was afraid that I lost half of my priming solution to the floor. All I did was RDWHAHB...