What can I do about my underbite?!

Nothing. hahha. We need more info.

Depending on your age, if you are young you can use your tongue to pull them back. Do this constantly and they should get better within a couple of years. That is what my dentist told me when i was in danger of getting braces in two years time. Because i took his advice, it saved me. If you are older i am afraid the only thing to do is go to a dentist. You might be able to take care of that with this years income tax.