i just used a item to turn a planet from barren to ocean.. now it has dissapeared ... can i please get it back thanks

The planet? It is still there. I bet you have "Barren" in the text box. Click the 'show all button' and i think it will show up. Remember, it will be in a different place on the list since its stats have changed.

You can always try searching for the planet by name in the planet tab, as long as you can remember the name of the planet. Or try searching for Barren planets (It takes the game a few minutes to update so it might still be listed as a Barren) and for Oceanic planets. Also try refreshing the game (Press F5), in case the planet really has gone missing and it was just a temporary glitch.

If none of that works, try Contacting The Developers and explain your situation.

I read this as "I just used an item... and now it has disappeared."

If that is what the original poster was referring to, those are one-shot items. They go away after you turn the barren world into an oceanic one.