I think Abv is going to be a product of how much fermentable sugar you have in the wort you are brewing and this can be easily derived by hydrometer readings. I would think that with 8# of LME, you would have had a higher OG,FG, and ABV.
If you did not take an FG when you bottled then you have no idea as to the ABV of your brew.
Take readings and then you will know.
BTW most of the OG ratings I've seen on LME recipes/kits have been a bit liberal. you may need to adjust to reach the OG they specify.