17% off for 1 wrong bit?

I've nearly completed my first week of my first class of the year. On Monday I turned in my first assignment, an SQL script that creates 2 tables and populates them with some data. The first table is supposed to use the primary key in the second as a foreign key for a field in the first. (Don't worry if that went over your head, it's not completely relevant.)

I forgot to put the constraint that the field in table 1 references the key in table 2. A single omission in several pages of work. The assignment was worth 12 points and the instructor deducted 2 full points for that omission. That's 16.7% for a single word missed. And if it broke things and nothign worked I could understand. But, everything worked fine, there was just no link between the two fields to enforce data integrity. I was a bit miffed, but wrote back questioning the grade and if I could make up some of the lost points by submitting a revised assignment with the error corrected. We'll see how that goes...