If it wasn't, all I can say is you need to water it a lot more! Depending on how much sun it gets, and how warm your windowsill there is, water it enough to keep it moist all the time, but not soggy.
My Heliconias are all outdoors in partial shade (I'm in Florida) and they really take off and shoot up when it starts to rain heavily - inches per day - here in about June. As long as the pot has good drainage (is there a hole in the bottom? I don't see a saucer) you really can't water it too much. But if it does start to grow, you'll need a bigger pot pretty quick!
These are my smallest ones, they're about 2ft tall when they're blooming. I have others that are 3ft, and some really tall ones over 5ft. tall.
