XY scatter chart - data points don't align properly on X axis

I tried to create a simple XY scatter chart where the vertical axis
represented the cost per gallon of gas and the horizontal axis showed each
month for 2008. (Although I thought this type of chart would be considered a
line chart, Excel considered this to be a scatter chart.)

Though I wanted each month to be displayed, beginning with January and
ending with December, the X axis on the graph reads:
Nov-07, Jan-08, Feb-08, Apr-08, Jun-08, Jul-08, Sep-08, Oct-08, Dec-08.
March, May, August, and October are omitted. Although all 12 data points
appear on the graph, none of the data points are aligned with the proper

Additionally, when I tried to display a chart showing monthly prices going
back 20 years, all the data points were displayed in one big clump, rather
than being spaced out over the 20 years. I had expected to see 240 data

I would greatly appreciate any help in solving these 2 problems.