Any time you are putting a bolt, nut, or anything with threads onto something else with threads you should always turn the object backwards 1/4-1/2 turn. As you turn it backwards, you will feel a small "click" as the threads on both items line up. Once this has happened you can start threading the parts together. The "click" you feel is the two end threads dropping into engagement.
I know it is too late for you, and in your case I know it is not your fault. The way I see it, you have three options;
1- Call customer service and get them to fix the receiver.
2- Run a tap of the proper thread through to correct the cross-threading, and be careful anytime you tighten the part up.
3- drill and install a helecoil then refit stock bolt.