In Jenga, what happens if there are 2 blocks on the top of the tower blocking the way for the 3rd block?
The rules on Hasbro's site say that you can touch other blocks with a single hand, and you must complete a 3 block story. I don't see why it would be unacceptable to either fix the top story with your hand directly to accept a third block, or nudge the top blocks in place with a block in your hand to complete the story. Clearly, if you are required to make a 3-block story, the blocks must fit across the top.

While stacking, always complete a 3-block story before starting a higher one.
You can touch other blocks to find a loose one - but if you move a block out of place, you must fix it (using only one hand) before touching another block.

This is a mass market game. The rules are written to be as easily understood as possible, not a game like Advance Squad Leader or Magic: the Gathering where the rules are written to close every possible loophole. The rules don't define what 'fix' means or 'out of place', but since you are supposed to create the top story with 3 blocks, those three blocks must fit on the story. The rules also don't prevent you from placing your top block perpendicular, but with nearly half the block extending over the edge of the tower, but I contend that a piece placed like that is &quot;out of place&quot; and is subject to the fixing rule. To fix a block is to move it back to its relative position in my mind. (Example: Top of the tower, center block.)
Several digital versions exist for iOS, Android, Wii, etc. You could always see how the rules were interpreted for those electronic versions and copy their behavior. The Official Jenga version for iPhone allows you to nudge any pieces you want during your turn to 'fix' them (or ruin them actually). The iPhone developers consulted with the original game designer Leslie Scott in the making of the game. In this implementation, a player could place 2 blocks on top to prevent an opponent from placing the third block of a story, but his opponent could just nudge those pieces on top to make room for his piece.

NaturalMotion Games worked closely with Leslie Scott, the inventor of Jenga, to create the most authentic Jenga experience ever.
“I’m delighted by how the team at NaturalMotion Games has so skillfully captured the essence and universal appeal of Jenga,  while adding new and thrilling dimensions to my original game.” – Leslie Scott