Garmin Forerunner 301 loosing data

Hi,

I just went on a 300k bike ride, and wanted to take my forerunner 301
to log the route.

Unfortunately, when i got home and downloaded the route into the
training software, it seems to have lost the first 100k.

It would appear that there is a maximum number of points it can record,
and then it loops round, overwriting the original points? The odd thing
is that my previous routes are still intact.

Does anyone know how i can solve this for the future? Will it help to
put in auto laps ever 100k or so? Do i need to stop, reset and restart
at about 200k, to capture the journey in two parts??? Is there anyway
to reduce the frequency of wapoint sampling to ensure i can get more
than 200k in at once?

Many thanks,
Mark.