Your SGA size is only 114M. The Variable Size is mainly made up from your large pool, java pool, and shared pool. You think you are allocating about 68M, but you must remember that oracle will allocate in granules. Also, there are other parameters that contribute to the SGA size. I think this looks about right for what you have specified.

If Oracle really is taking 630M at startup, I would look at your kernal parameters. You may have the minimum shared memory segment at 640M or something.