smoothing function is adding extra data to my EDX spectrum

I have EDX line scan data (from Aztec) for two elements x and y along a length L. The scan length is originally 1.7mm long in a .csv file. After using the smooth function

C1  = smooth (L ,C, 0.1, 'moving')

or any other smoothing operation (lowess/ loess) for that matter, the spectrum suddenly has data to a length of 2.5 mm. I have checked the smoothing functions effect on the data, by individually applying the filter to x or y, and as suspected, its the smoothing that somehow calculates extra data points beyond what has been recorded by the detector. Is there any way to fix this problem? Thanks in advance for your help.

[Walter Roberson]

Please show your smooth() call. The call you show is not a valid smooth() call. Your L might correspond to x, and your C might correspond to y, but spans for moving average must be odd positive integers.