You fell victim to the shoulder bolt strip-out trap I see. The unsuspecting think those bolts are turning real easy when they are just compressing the big rubber washers under the heads, but then the steel shoulder fetches up on the cam housing and it abruptly stops turning. At that point you just move it another 5-10 degrees of rotation to snug it.
To repair it you would need to helicoil the stripped threads back to the original size, since you will need to use the original special bolts to hold the valve cover in place and make the proper seal. Repairing would be cheaper and better too, since you are also replacing half the camshaft bearing surface. You might do better to take the parts to a machine shop to do this repair. Don't mix up the left and right parts.

 

E-Z LOK thread insert or Time-Sert is my first thought.. they have more meat than Helicoil
DIY or have local shop install..
Mark the camshaft caps to assure they go back where they came from..

 

Thanks for the insight! I will definitely try either the helicoil or ez lock or timesert. And this time I will make sure to tourque it properly. And again, thanks for the help!