Using brewing enhancers can mean the final gravity (FG) reading ends up higher than expected, which is fine.

Sometimes when the gravity is higher than expected it can be commonly referred to as a "stuck fermentation" and can have a couple of causes.

• The simplest cause and probably the most common is temperature. A significant drop in temperature can cause the yeast to go dormant and settle to the bottom

To fix this move the fermenter to a warmer room and try swirling the fermenter to stir up the yeast and get them back into suspension and active. 

• Stress to the yeast can also cause it to finish early. This can be caused by not enough yeast cells in the beer or major temperature swings. 

Try to keep the fermentation temperature as consistent as possible and it is always a good idea to add a second yeast packet for fermentation. 

For some tips for storage temperatures, see here.