Any time you see your hash rate on a pool page, remember that it is JUST an estimate.  It is guessing based on how fast you are sending shares.  And if a pool has their stats set to update quickly (like every minute) then you can hit spots where you send a ton of shares quickly and it makes it look like your hash rate is much higher than it actually is.  The other extreme is that you can see half or less of your real hash rate.  This is also affected by vardiff, until the size of shares you submit stabilizes.

tl;dr- don't be concerned in the short term if your hash rate is wrong.  Give it time to stabilize!