This should probably have been in new player help, but I'd suggest there's no way you did everything possible on Tatooine and left at level 25.
There are 4 main types of quests: your class quests which you have to do, a main planet-based quest (usually working for the governor or other local official), random side quests at each outpost you visit (including group heroics) and the Bonus series for most planets which becomes available after you've completed the main planet quest. The Bonus series will be given to you in or around the shuttle bay as you're leaving the planet if you already did every part of the planet-based quest for the governor.
You may have completed your class quest on Tatooine, but there's no way you finished the others and leveled out of
Tatooine that low. Just go back and look on the map more carefully for quest-givers, particularly the planet quest in or around the main space dock which is the bulk of your experience on the planet.
If you didn't complete the planet quest and left the poor governor in the lurch, do that and by all means do the Bonus quest, which offers the highest rewards for time spent in the entire game. The Bonus series is basically where the game just heaps gads of money and experience on you to make you feel better about yourself.