scatter chart and column chart won't align

I have a graph with one x axis, and two y axes. The primary axis is a scatter chart and the secondary axis is a column chart. However, these don't align on the x axis, even though they indicate the same x value. (Towards the left side of the graph, the primary data point is to the right of the secondary column; towards the right side of the graph, the primary data point is to the left of the column.) Since these data points are for the same value as the columns they correspond to, I need the data point to be aligned in the middle of the column, not to the right or left. I'll attach a sample. Thank you, in advance, for any assistance.

Changing it to a line graph does fix the problem. However, then the x-axis labels aren't so consistent or nice (1, 6, 11 instead of 5, 10, 15). Any suggestions?

Thanks, Andy! I also got the tip to make it a line graph, instead of scatter, and that works. The data points and columns are aligned now. But the x-values are not as nice and consistent (1, 6, 11 instead of 5, 10, 15). Any suggestions there?

Oh wait, is that the question you were replying to? I can't find where to enable a secondary horizontal axis...