OCS is a big deal and tough but it's not that big of a deal or tough. Listen to what your OSO has said, read some blogs as jhoward suggested, and keep pting.I am afraid of being dropped from Marine OCS, what can I do to prepare? I like to think I am capable of this, but I am afraid of DORing without saying it.
That's what OCS is for, to evaluate those things. Just let the program work. You'll get there, learn allot, and if you apply those things you will probably be fine. Few get dropped for leadership; if you had little to no leadership potential, you wouldn't have been selected.
Control what you can control. Don't worry about what you can't.