Can what the questioner invoked upon herself be realized—after her exams—of her not achieving good grades and a total score in them, due to her return and relapse into masturbation after having made a covenant with herself to abandon it?

Masturbation is a forbidden act, and a Muslim invoking evil upon himself is prohibited, such as praying for failure in studies. Whoever swears not to commit a sin then commits it, must offer expiation for breaking an oath, and must repent from the sin. And whoever invokes evil upon himself with the intention of urging himself to do something or to refrain from it, this falls under the ruling of an oath; if he breaks it, he must offer expiation for breaking an oath.