Could my elastics be causing a slight underbite?

I've had braces since October of 2013 and I've been wearing elastics 24/7 since April of 2015, and they have helped my bite tremendously. I used to have a very large over jet, and now my teeth meet together, but my top teeth don't overlap my bottom teeth at all, there are gaps. I was told that when you get into the final stage of having braces (I'm scheduled to have them taken off on April 2nd) your top row of teeth should overlap your bottom row slightly, forming a natural overbite. But, I have also noticed that the more I wear my elastics, the more my bottom jaw is coming forward more than my top row of teeth. This is a slight change, but I worry that it's going to get bigger. The last orthodontist checkup I had was three weeks ago, and the next one is coming up on January 11th. Last appointment my orthodontist didn't specify with the nurse whether I need to keep wearing my elastics, and so it was her that made the decision, and she told me to keep wearing them 24/7. Do you think it's possible or likely that these elastics are giving me an underbite? I don't know if I should keep wearing them 24/7 or just stop wearing them until the next appointment/until I can call them on Monday, as they're only open on Monday, Tuesday and Wednesday. Thanks for your help.