A student is instructed to prepare exactly \(250.0 \text{ mL}\) of a \(0.100 \text{ M}\) \(\text{CuSO}_4\text{(aq)}\) standard solution using solid copper(II) sulfate pentahydrate, \(\text{CuSO}_4 \cdot 5\text{H}_2\text{O}\) (molar mass \(250. \text{ g/mol}\)). The student correctly calculates and measures \(6.25 \text{ g}\) of the solid, dissolves it in approximately \(100 \text{ mL}\) of distilled water in a beaker, quantitatively transfers the mixture into a \(250.0 \text{ mL}\) volumetric flask, and adds distilled water. During the final dilution, the student accidentally adds water until the meniscus is approximately \(5 \text{ mm}\) above the calibration mark on the neck of the flask. Which of the following correctly identifies the effect of this error on the actual concentration of the solution and the appropriate corrective action?