Is it bad luck? Or a good deal?

So I went shopping for a dress to wear to a bachelorette party. I went to Ross's dress for less. I found a pretty black and gold dress and heals for the bachelorette party.. But I also came across a very pretty off white gown that I'm assuming was a homecoming or prom dress as it was very glittery! For $20...I'm thinking this could be my wedding dress!!! For starters I am not materialistic.. I would marry that man in a garbage sack of I had to! Now here's the catch.. I'm not engaged.. However I know it's coming within 6 months.. I know this because he and I talked we've been together for a few years and we have a daughter together! So what's your take!? Bad luck to buy a wedding dress before an engagement is even official OR is it a good deal :) I'm not a huge fan of throwing money down on something I'll wear once.. Id rather put more money into the reception or a honeymoon than a piece of material I'll wear once... ( I know I look horrible in this picture but hey I just had a baby 3 months ago.. I know spanx will be a must 😂)