So you probably have a triple scale hydrometer, which has 3 different ways of measuring the alcohol by volume: specific gravity, Brix/Balling, and potential alcohol. Just pick one scale and stick with it. Potential alcohol is easiest. Just subtract the smaller final potential alcohol reading from the larger starting potential alcohol reading. For example, with a 6.5% abv starting reading and a 1.5% abv final reading you would have a beer with 5% abv... simple right? Using the other scales requires either consulting a chart or using an equation (or an app) to get your abv reading. Also be aware that the hydrometer is calibrated to 59 degrees F, so if your wort or beer that you are testing is significantly hotter or cooler than that you need to correct for it because your reading will be off.
FYI, you will never get 100% attenuation (conversion of sugars to alcohol by the yeast), usually it will be between 70% and 80% of your starting gravity depending on fermentation temp, yeast strain, aeration, etc...
And yeah, you screwed up by not adding priming sugar, but all brewers make mistakes in the heat of the moment

The easiest solution may be to get some Coopers carbonation drops from a homebrew store and open up all your bottles, drop one in each and recap them. Otherwise they will never carbonate (assuming your beer had fully fermented before bottling).
Word on the street is that about half of the dry yeast population is lost when sprinkled directly on the wort compared to properly rehydrating them first. (Even though most beer kit instructions tell you to sprinkle it).
Good luck!