Don't get discouraged.
Although it's unlikely that you gained muscle, it's also very unlikely that you gained fat. When first starting an exercise routine, you often retain water in your muscle tissue due to soreness. Eating a lot of salt, the time of day, the time in your cycle, etc, can all cause your weight to fluctuate as much as 5 pounds-- all with no change in your lean & fat mass.
Look at the trend of your weight-- I can guarantee that if you follow your WW plan & exercise, the trend will generally be downward (barring some kind of metabolic disorder). But it probably won't be linear-- there may be some random scale jumps in there. Don't forget the big picture- you're making some awesome changes in your life, and they will have positive results!

__________________
Most wanted jeans: Green Rainbows! 26/27
Also looking for Paige petite Robertson 27 & Ellis Island Lexie 26 on the cheap