Same prom dress

Hi, I'm a 15 year old girl from the Netherlands! And I'm finally gonna have my prom night. The problem is... i bought a very similar prom dress to the one my friend boutght. my friend brought her prom dress back in April and I bought my dress just this month (may). Please keep in mind that my memory is not the best. So when she showed me her dress in April , I had already forgotten what it looked like. And I didn't really ask after that, so I brought my dress. When I went to school I was telling her alllll about how I loved my dress but that I had to keep it a surprise. But after her begging and begging to show the dress, I eventually did. And she stopped. Looked me in the eye and goes: "I think we have the same dress... ". And my heart sunk al the way in my toes. Because she SHOWED me her dress and I still bought a similar one😭. Now, I don't work so I don't have the money to buy another one ore to buy something to make it look different and my mom won't buy anything either because "she has been your friend for so long I'm sure she knows how forgetful you are." But I feel horrible about it. I'm even considering not going to prom anymore. What should I do?

(Ps: I already told her about it, and she said it's fine, but I'm not sure if she means it.)