You will edit the graded essay later in the term. Correctness and formality are two totally different linguistic continua.
Formality is a function of such elements as situation, audience, and genre.
For various reasons a person might want to say indolent rather than lazy . Use a head of your last name and page number at the top right corner. For example, I grew up in the Midwest with Canadian parents whose language was identified as vaguely foreign by my peers. These and many other little usages, I guess, were supposed to make us better. It's absurd on a linguistic level I now realize.