Usually, when you have more than two points, they'd like you to plot a line, and determine a relationship between absorbance and concentration that uses all points. Did anyone mention how you were to do that? In your ratio, you're only using one point -- can you really be so sure it's correct, that you don't need any others?
P.S. You said you made 5 solutions, but you only posted 3. You not ignoring the others, because you don't link them or think you don't need them because they're far from the unknown absorbance, are you?