Is it permissible to marry a girl before she enrolls in university for fear that others may propose to her, knowing that I have not completed my education, am approximately 18 years old, and my salary is 3000 Saudi Riyals, and will my family and her family agree to this marriage?

Marriage is goodness, tranquility, and a means of preserving one's chastity, but it requires thought, deliberation, and consultation. The parents' viewpoint is worthy of consideration unless it conflicts with a weightier interest. If the parents' refusal of the marriage is based on a valid reason, then obedience to them is obligatory, unless one fears falling into temptation. If marriage to her is not possible, there are many other women, and goodness may lie elsewhere, for: "And perhaps you hate a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah Knows, while you know not."