If you can do that without stopping, just keep doing it, then when you can do it twice, the 26 miles in June will be a breeze.
Depending what you use to record your trips depends on what data you can use, i started off with a simple cycle computer which did speed, avg sp, distance and time, using a site like gpsies I had an idea of the elevation gained.
If you have smart phone that can use strava or endomondo you can upload to these sites and they will give you other data, both sites allow you to export the rides so they can be used on other sites or applications.
I keep core data, like distance, time, elevation, H.R. and cadence and weather in spread sheet, which then works our varies other things like ft/mile, difficulty gear" ect.... ( I am a bit of stats freak, though not a very fast cyclist).