Did you use straight 3% Hydrogen Peroxide Solution?
That might be too strong. Usually I put about a tablespoon of 3% HOOH in a cup or so of water for my soak.
For what it's wort, I always soak them in 3% H2O2 for 2-3 hours, then rinse and soak in tap water for another 24h or so. I usually have really good germination rate without any fungus related issues!