don't have a full screen?

Generally it is best to set the TV and a decoder/recorder box to 16:9 or “original”.
Unfortunately you have not posted enough information.

When asking about fixes always state the model of the appliance. I've goggled "rca" but this has not helped to narrow down which TV you have.

The same model of TV can behave differently in different countries. TV questions on "how to mend it" include questions from UK, USA, New Zealand, and probably others. Unfortunately you have not stated which country the TV was sold to.

You have not stated how you are receiving TV. E.g. It could be from a cable/aerial/satellite box, or it could be directly from a cable/aerial/dish. If it is from a separate box then how it is connected?

Unfortunately you have not stated what you have tried. If you had stated what you have tried this would help those trying to help to understand your real level of expertise and also help to narrow down the possible cause.

Because you have not provided this information it is not possible to state a fix.

NS (UK)
January 2013