Perhaps the songs you have put on your iPod so far are at a very high Bit Rate (the format of the file) or they are very long.
In iTunes, highlight one or two of the songs on your iPod and for each one, select File/Get Info/Summary and look at the field named Bit Rate. What does it say?
Apple's figures for the number of songs you can put on an 8GB iPod Touch are approximately 1,750 songs. But that assumes that each song is using a Bit Rate of 128Kbps and is three (or is it four?) minutes long. So if you are importing songs at a higher Bit Rate or every song is eight or nine minutes long, that will reduce the total number of songs you can fit on the iPod.
Also, check the import settings in your iTunes, typically, people use: Edit/Preferences>Import Settings/Import Using>AAC Encoder>High Quality (128Kbps) or the .../MP3 Encoder/Good Quality (128Kbps).
You should only use the higher Bit Rate settings if you can hear and appreciate the difference in quality.