You can not mix the varying length data series across the axes.

A line chart has a categorical X axis. So either 1 to 28 for the number of students. Or 1 to 245 for the number of points in the first for series.

If you do mix series on axis then the students information will appear in the first 28 slots.

The only way I can see you combining the information is to some how convert the 245 values for the series except CO2 to 28 values.