I downloaded Orbot on my tablet and I've been reading about the Tor network and I looked up "Is running Tor illegal in the U.S.". I found out about exit-relays and the Orbot app said something about exit relays when I set it up. Does just running Orbot mean I am running an exit relay?
No. By default, Orbot will not run a relay/exit/bridge. You may have seen one of the circuits Orbot built, which show the path your data will go through when using Tor.
Unless you have changed your settings to become a Tor relay, you should be okay.