Broken bolt in the head!

[Nima]

Well I bought this chrome vavle cover bolt package from a store close to my house. I was happy that everything was going well with my weekend project. So far I have changed the intake, cleaned all over the engine and ready to put valve covers. I got everything ready but I had a little problem with lining the cover holes with the head holes. Finally everthing lined up and I started inserting the bolts. They were not half way in that they stopped, all of them!. Since I was sure that I cleaned (tapped) all the hole before, I guess I pushe a little hard and them bang! one the bolt broken in the head. After that whenn I compair the new bolts with the original one, I noticed they are a lot longer! almost twice. I don't know what the hell is my problem with differnt legth bolt on this project!. Anyways,I tried to drille out and tap it again which tap broke in it!. Now what? Please give me some clues since I am very scared! Thanks