There are three things you can do to botch the bullet guide installation.
You could drill the hole in the wrong place. This could make proper placement of the bullet guide impossible. Be sure you're drilling in the right place, and use a center punch.
You could drill the hole all the way through the receiver. You don't want an unnecessary hole in the bottom of the receiver. When the bit cuts through the trunion, stop drilling.
You could break the tap off in the hole. No permanent harm done, but a broken tap can be a real bitch to get out. Keep plenty of oil on the tap, go real slow, and back the tap up a quarter turn or so for every half turn you make. If you put too much strain on the tap, it will break.
If you are not sure you can do any of these steps, take it to someone who is sure.