Question about Project Hail Mary's physics (minor background spoilers)
So I recently read Project Hail Mary and watched the film, and first of all, if you haven't at least watched the movie yet, what the heck are you waiting for?! lol. But anyway, one of the plot points of the story is that because Rocky's species was apparently completely unaware of Relativity, they ended up bringing far more fuel than they actually needed to reach Tau Ceti, because they were assuming that Newtonian physics was the way the universe operated. As a result, Rocky explains that he was baffled both that the trip seemed to be a lot shorter than he expected, and required far less fuel.
But shouldn't that have resulted in them having LESS fuel than they needed rather than more? Since the closer you get to the speed of light, the exponentially more energy it requires to go faster/keep accelerating, whereas under Newtonian physics it would be linear? Normally Andy Weir does his homework regarding stuff like this, so I want to give him the benefit of the doubt. But I don't understand how this could be possible given my admittedly layman's understanding of Relativistic physics.