It sounds too convoluted and second hand for me to do too much "planning" and worrying about it if I were you. When some of these things were said (could have been before you renewed your efforts?) and that they are conflicting and that your friends are personally involved, it could be partly their telling of the whatever they have heard and maybe they have some sort of thing going themselves; it is very suspicious to me that Amy was supposed to interview for your job but did not show and that Beth is telling you what Amy is being told by your boss when, if it were you or me and we were Amy, we'd just tell you ourselves?

In all my jobs I have usually had 3 months to learn a job well. It sounds like you are doing yours well now and nothing is actually happening, other than your boss saying he is pleased with your work now, since you corrected your mistake. I am very suspicious of Amy and Beth, friends or no, giving you conflicting information and stirring you up, what good could come of it? And Amy supposedly interviewing for your position? Who does that to a friend? Maybe they have a problem with you or your boss or maybe there is some truth to what they say but it is badly told or exaggerated, etc. I would not talk about work with people not there/part of it?

If they don't like your boss, maybe they are trying to get you to confront him or cause a scene, etc., cause him difficulty. I would be very suspicious of "friends" that are meddling with my work and gossiping when they are not part of the relationship with your boss and you. Maybe they just think it is "funny" and a harmless prank but look how upset, confused, anxious you are? Who does that to a friend?