Heart of Darkness is actually a really good book. My English teacher made that lesson more interesting for my class by playing Apocalypse Now. How long is your journal assignment? It helps to know what you’re going to write about before you begin. “Literary elements and what they mean” is a pretty broad question, and if your teacher wrote that question, they phrased it in a pretty boring way. You could write about, say, tone- how the book keeps getting darker and more ominous as you go along. Just go through the book and find a few quotes that support that, then write about them. Diction, which means word choice, is easy enough to write about. It’s really simple to write, “Author X is using diction to show Y” and pick out some words that show your point. For Heart of Darkness, most of what you write will probably show that things are becoming scarier and less civilized.
It’s nerdy, but it also helps to focus on the sense of accomplishment you get from finishing something. I hate my math class, but I feel really good after finishing a bunch of math work. You can also think of what you’re doing as not boring- try to feel interested in it instead of resisting it, and it actually does get easier.