The big hammer approach is to quit the Kernel
(Kernel menu) or exit Mathematica and then
start a new Kernel or relaunch Mathematica.
The small hammer approach would be to use
SetOptions[Graphics3D, ...] to reset the options
you have changed back to the original. If
you don't know the original you could execute
Options[Graphics3D] before you make your option
changes to see a list of the defaults. You may
also need to look at the options of the specific
commands that you are using (Plot3D and so on).
PS: is strikes me that something like
originalOptions = Options[whatever]
would give you list of the options for whatever
which could be used in a command like:
SetOptions[whatever, originalOptions] to reset
the options to the original.
Warning! I have not tried this and don't have a
copy of Mathematica handy to test it out.