There are gaps between the dates plotted in my chart.

If the datasheet data for the category axis contains date number formatting, Microsoft Graph automatically uses a special type of axis in your chart called a time-scale axis. A time-scale axis shows a blank category for dates for which you have no data. If you do not want to see these gaps — for example, if you have data for 1-Jan, 15-Jan, 3-Feb, 12-Feb, and 2-Mar, and you want to plot the days next to each other — you can change the time-scale axis to a standard category axis. On the Chart menu, click Chart Options, click the Axes tab, and then click Category under Category (X) axis.