I'm so sorry you had this experience. Sadly Target can't control what sort of unaccepting people might be in their customer base, even if the store and employees are allies. This was just a very bad encounter in many ways, a perfect storm of yuck.
Some things to consider...there are cis women who cannot become pregnant that feel that very same isolation and that very same grief at the prospect of being left out of the "sisterhood of pregnancy", missing out on those conversations and feeling included in that aspect of motherhood. They can run into thoughtlessness and casual, ignorant remarks that ruin their day, too. It does not make them any less women.
Another thing to consider...some women are just not nice, not accepting, and not friendly, even to other cis women. Please try not to take those nasty people to heart, or personally, or think it's *your* failing. It's not you, it's them. There are plenty of nicer and wiser women that are better friend material, and they WILL accept you as one of them. Many of my close friends are cis ladies that I know would never close someone out because of the circumstances of their birth.
They are out there, a lot of them, but just like making friends in any circle, you have to weed out the rotten ones and pick out the good ones. It's scary even without the stress of transitioning and worrying about prejudice, so you have an extra hard row to hoe, but I promise you that you are not doomed to a life of being shut out by women, or never being accepted as one of them.
I don't know if this will be any help, but this reframing helped me years ago when I was being bullied and felt like I would never be accepted by *anyone*. You know how, in nature, some venomous or poisonous animals are brightly colored as a warning that they're toxic and dangerous and should be left alone? I began to see nasty, rejecting behavior as the human equivalent of neon colors, and think of them as a gift. Those women in Target yesterday flashed you some bright, nasty colors and let you know in no uncertain terms that they are poisonous, so hey, great warning--even if you were cis, their friendship would be worthless. Like I said I don't know if that helps others but it made me feel a LOT better about other people's nastiness, and in realizing that it wasn't me, it was them.
Seriously...it's not you. It's them. They are awful, and you had the misfortune to run into them, but I promise you that they do not represent Womanhood.
*hugs*