So backstory,  my boyfriend got me this really pretty necklace for Christmas, nothing expensive I'm pretty sure it was like 10 bucks. A month or so later my older sister [24F] got this ring that looked super similar to my necklace, like it looks like they're from a set. 
I asked her about it and she said something like "I saw it and thought it was so pretty and it matches your necklace!" That doesn't really bother me all too much, I don't care what she wears although it is weird seeing a replica of my necklace on her hands. 

Later, she showed my mom the ring and then said "oh all we have to is get Younger sister [15] earrings and we'll match! Wouldn't that be cool?" 
I just told her "i mean yeah that'd be cool but maybe not something that my boyfriend got me?"
She just kinda seemed offended, not horribly angry but just bothered ?
It came up again the next day and i just didn't say anything
When I told my younger sister what happened she at first agreed, until I told her my boyfriend got me the necklace and then changed her mind. 

This hasn't been a huge deal, but I'm just wondering if I'm actually in the wrong? Don't get me wrong, I'd love to get matching jewelry with my sisters, but this necklace has meaning with my boyfriend, not them. 

So, AITA?