Is there a way to go back in time(about three or four hours), to reset the Mac, the way it was? I don't have an external hard drive, so no "time machine". Thanks.
The Local Snapshot feature may help if Time Machine is on About Time Machine local snapshots - Apple Support
More details about Time Machine with External Drive. Has good overall info about Time Machine and how to use Mac Basics: Time Machine backs up your Mac - Apple Support