Answer
The Aldhyde Stretch in IR will appear as two peaks at 2700 and 2800 $cm^{-1}$ plus the carbonyl stretch around 1725 $cm^{-1}$.
The Carboxylic Acid stretch appear as Broad Stretch from 2500 to 3500 $cm^{-1}$ Plus the carbonyl stretch around 1710 $cm^{-1}$.
Work Step by Step
Simply
1- if Aldhyde instead of ester it will give us stretches at 1725 $cm^{-1}$ as in the spectrum with us, but will not give us the saturated C-H stretch just before the 3000 $cm^{-1}$ and will give us stretches of aldhyde at 2700 $cm^{-1}$ and 2800 $cm^{-1}$ (two peaks there).
2- And If there is Carboxylic Acid it will give us the Carbonyl stretch as usual, plus the broad stretch from 2500 to 3500 $cm^{-1}$ of the hydroxyl group (-OH).
So we can rule out the presence of Aldhyde and Carboxylic acid easily.
