I e-filed but realized I forgot to enter something that impacts my federal tax due (not state). If my tax return is still accepted, can I use Turbotax to make the correction?

I'm assuming/hoping that the return will come back rejected since my filing amount was incomplete/incorrect, but in case this error isn't caught, can I use Turbotax to file an amended return? If so, how? 

And if not, what is the process? 

Also, what will happen regarding the amounts? For example, suppose the following:

- Fed tax due: $100
- Fed tax payment I submitted (due to forgetting to add  some information): $60

When I file an amended return, do I pay the full $100, or the $40 difference remaining? If the former, how will I get the $40 back?