Hi haeyu14, and congratulations on your weight loss!!
Unfortunately I don't have anything to say other than what has already been said... I once read that everyone has a fantastic set of biceps and triceps, they're just covered by fat. Until you lose the fat "blanket", you probably won't see much of a difference, even if you did work your arms with weights as often as possible. (That's every second day, btw... never work the same muscle group two days in a row.)
So, cardio is the way to go. But try to move your arms as you are doing your cardio. If you can, try out a class that has an all-over workout that also works your heart, such as boxing or other martial arts, boxercise aerobics etc. Those types of classes can also be low-impact. Push ups, if you can do them, are also good - if you keep your arms closer together it works your triceps more. Tricep kickbacks, hammer curls, shoulder presses - all of these will help eventually. It's better to use free weights than the gym machines as well, since you work more stabilizer muscles in the process.
But don't feel discouraged, no matter what. Everyone loses weight differently... I personally hate my bat wings!! lol

And I've boxed for years. I just have to lose the weight. So it's a slow process, and you may need to have surgery to remove the excess skin, as ShrinkingChica said. Be proud of yourself for how far you have come!!!

And if it makes you feel better, you can see if you could get a stole or a shawl to wear with your dress, and I'm sure you'll look fabulous!!
