One of the primary differences between typical people and people with OCD is that your average person doesn't commonly have an "amnesiac" type of memory. That is to say that they know when they do something wrong and can recall whether the memory is true or not. For example, I'm sure you can remember on a daily basis if you went to the shops or not and you are aware that it is true, you wouldn't sit there questioning it.

The element of uncertainty and questioning is a key principle of false memories due to the fact that your brain realizes that something doesn't add up/make sense. Thus, it begins questioning whether or not you thought/acted in an immoral way. It does this because your brain thinks "Hang on, I don't remember saying/thinking that about so and so....or did I?". The questioning aspect indicates that there is something wrong with the specific memory and in people with OCD this means that the memory is almost 100% certain to be false.

Thus, if you have to question the memory at all it's a key tipoff. I assure you as someone who doesn't have OCD symptoms or false memories anymore that I am never unsure whether I committed an act/ thought something or not. Whereas with OCD it used to happen constantly.

It makes perfect sense what you're saying, and all I can add is something that I remember someone once saying about OCD, which went something like this: "If you knew the memory was false then you wouldn't have OCD to begin with, would you?".
It is the questioning aspect that always drives someone with OCD and ultimately, the only way to really rid yourself of it is to stop questioning everything and just let go. This is usually incredibly difficult for someone with OCD, but is always the first footstep on the path to ridding yourself of it.