You're doing O. Chem wrong. Don't *memorize* the net result of a transformation, or you'll just memorize thousands and thousands of reactions. It's like physics: don't memorize the net equation of all the forces acting on a body for every situation, know how to derive them!
Approach this problem step by step, draw the electron-pushing and the intermediates/transition states, or you will be hopelessly lost.
Grignard Reagents are effectively "R-" or nucleophilic alkyl chains. You have an electrophilic carbon here (i.e., carbonyl C), so the first stop is going to be a nucleophilic addition to the carbonyl to form a tetrahedral intermediate, stabilized by MgX cation. Acid work-up will produce a secondary alcohol (since you're starting with an aldehyde).