It's hard to troubleshoot this without seeing your data sheet or where the x-axis data came from, but if you entered the data for the date column like this:
Then Excel will default to interpreting those as days since the beginning of "the era." You can cure this by entering the dates in full, like this:
Additionally, it appears that your graph is ending in August (or maybe early September). If you have fewer than 365 observations -- because, for example, holidays and weekends are excluded -- then, again, inputting the actual dates will help.
If you already have input the dates, it might be that your graph isn't using those cells as the x-axis labels. In that case, you can click on the graph, then "select data," then specify "horizontal (category) axis labels."