unfortunately you cant unlock it now you have forgot the code, it is a security feature designed to deter theft. Imagine if someone stole you ipod and then could just reset the code and steal your data?
You will need to reflash it using iTunes, plug it into a computer with iTunes installed. Hold the Power button and the home button together until it reboots, release the power button but keep the home button pressed.
iTunes will say it has found an iPhone in recovery mode.
Restore it to factory defaults, if you only got it yesterday then you wont have lost much!