Sorry to read about your investment mistake. We all make them, we cannot win them all. Sometimes we sell early and sometimes we hold on to them for too long.
Do you remember how much you paid in the ICO for the 300 ETH?
This is a very old ico but some new sites have already made the detail of ethereum ico like this one https://icodrops.com/ethereum/
It looks like ethereum ico is not offering a bonus mechanism for early investors or i may wrong about that because there's only a little information about that but it does not specifically explain a lot about ethereum ico and there's a bonus mechanism or not.