Hello mouse detective,
Welcome to the Board. I struggled with this same issue for years and finally created a spreadsheet where I could input the date, scores, the lane we bowled on, etc. The spreadsheet would calcuate the season average, high score, etc.
Then, after doing all that work, I found a FREE product on the internet that was even better. In addition to the above, it tracks your average on each pair of lanes, what percentage of your games are in the 150's, 160's, etc and the same percentages for series, etc. If you want to go to the trouble to input the data, it also can track your percentage of spare conversions. It is many times better than what I created for myself. It also is set up for leagues that bowl 4 and 5 games as well as three games.
When you first set it up for your league, it will ask you how many teams are in the league, how many weeks you bowl, and on what lane your league starts. So you might have to wait until after you bowl the first week to set it up. But go ahead and download it, play around with it, and become familiar with how to use it. It is really a great tool to keep up with your bowling stats.
The best part, of course, is it is free! I have included a link to the site below. I used it when I bowled, and highly recommend it. Good luck with the spreadsheet and your game!
http://www.bowlingfans.com/downloads/stattracker.shtml
----dave