But you missed the straighten tool to get the horizon level while you were there
(Yes I'm a hard task master, just ask Wendy)
OK, a bit more helpful
Select the tool, click exactly on the horizon on the left, move mouse to right hand side (dragging the string), click again exactly on horizon, ACR will now make that line horizontal by twisting image, it also does the crop when it opens in Elements or CS. You can see the finished effect by moving to another tool, like the magnifying glass, before leaving ACR.
Cheers,