No. It 100% can be your actual past *if* you being in the past was always a part of the timeline. Nothing in the movie contradicts this. Your interpretation fits the movie, too, but it is *not* the only possible interpretation of what the movie says, no matter how many times you guys repeat the same argument over and over again.
I know I said I was done with this pointless shouting match, but I think this illustrates the fundamental sticking point.
Right here, you're going on the assumption that the usual fictional rules of time travel applies, when they do not. There was even a scene in the movie where they very explicitly refuted this notion and repeatedly explained the rules for this time travel story.
It doesn't matter if people knew or didn't know if Steve was Peggy's husband or not. It's immaterial. Steve isn't Schrodinger's Cat. Whether you look in the box or not, the universe has already made up it's mind and it's based on mass and energy interactions, not human awareness.
Put it this way: if Steve Rogers was Peggy's unnamed husband then it wasn't the Steve Rogers we know; it'd have to be some Steve Rogers from another universe, one that for some inexplicable reason sat out the 20th century with his thumb up his arse, sitting back and watching his wife struggle against forces in utter futility. So fuck that Steve Rogers.
It's not physically possible for it to have been Steve. It's not a happy ending for it to have always been Steve. And it's not possible for things to have played out as they did with
this guy just hanging in the background. It's not in his character, it's not good storytelling and the science as presented in the story doesn't support it.
And with that, I'm really really done! If you guys want to continue dying on this hill, have at it! Honestly, I don't see the point.
ETA: for those still struggling with the concept, here's a fun video by a guy that knows the actual science behind it.