You haven't been scoring low enough to lower your average. BTW, just in case you weren't aware, level has nothing to do with average.
I'd have to disagree with Jim. Since you average is 67.52 you'll need to score 33 or less on 9 holes. 34 will not effect it. You'll need to score 66 or better on 18 holes to lower your score enough for you to notice. 67 on 18 holes will lower your score, but we're talking a few hundredths of a point.
Practice, practice, practice. Best of luck!
- Steel