When the newest leaf on my giant bird of paradise started to unfurl, I (perhaps foolishly) decided to help it by pushing the edges past the obstacles created by the existing stems. Now the leaf is fully unfurled, but the stem is too short; instead of arching over the previous leaf, it sticks straight up and has hardly any space for another leaf to bud. I'm afraid I may have caused the stem to stop growing prematurely by causing the leaf to unfurl too soon, and I wonder if there's anything I can to remedy the situation. This is a plant I rescued a couple of years ago and I'd hate to think I ruined it out of stupidity. Any help would be very much appreciated.

You didn't do anything to cause the leaf stem to be shorter. It most likely is related to the weather while the leaf was developing.

The most common reason that the leaves get "stuck" while unfurling is because the soil has gotten too dry at some point during the leaf's development. When properly potted, B of P is hard to over water. Misting the unfurled leaf with soapy water will sometimes help it along. There is a technique for manually assisting the unfurling, but it is too complicated to describe so I don't recommend any manual assistance.