What computer operating system is involved?
If your Premiere Elements project preset does not match the properties of your source media, then you start a new project and select the project preset that matches the properties of your source file.
If Premiere Elements does not have a project preset for the match, you can import the file and then scale it to the space created by your choice of an Adobe project preset. Or, you can create your own project preset using the principles used in the following
As for export of the Timeline content...explore the Advanced export settings under Publish+Share/Computer/....... and see the Advanced Button/Video Tab of the preset selected.
Please consider and supply more information on export side for further details on that.
Any questions or need clarification, please ask.