Matlab multiple scatter plot, add average and stdev

I have 99 "pairs" of XY coordinates which I plotted nicely to get a graph which looks like this:

http://ift.tt/1vPnuL6;gda=1425397758_35a3540fe9b0b3e07093ca03afd06a12 (apologies for the awful photo!)

Each of the 99 lines shows the trajectory of a marker in time going around a corner. What I would would like to do is to add a line for the "average" trajectory in a thicker, more noticable line and to add the standard deviation in, say, grey.

I used Excel to calculate the average and stdev, so I have the values I need (I hope) but as each trajectory is not the same length I assume my calculations are probably incorrect.

Here is an example of what I mean: http://ift.tt/1GE8zom;gda=1425348732_37607e9d38cfd8a5b731db4158e2ce33

What I did was take the average of each of the yellow X values continuing to the 99th X column for each row (so in Excel this would be (A2+C2+E2+G2+I2+K2+M2+O2+Q2+S2....)/99, then (A3+C3+E3+G3+I3+K3+M3+O3+Q3+S3...)/99 and so on. As the number of rows are equal for each trajectory I wonder if this has a knock on effect on the mean and stdev.

Many thanks for taking the time to read this!