Even though I did not got for a pixel-precise solution myself, I think you missed one essential part of the body text. It is indented by a margin as well. Your text is missing a margin on the left and right. Thus, your text is longer than in the example.
You forgot the box-shadow that is visible
The task also gives line-height and letter-spacing which is not in your solution.
The width of the box also needs to consider margins and padding. Thus it is much wider than the box in the task.