Assume for a minute that you had the physical strength to do it. That you had the ability to dig to China (or to the opposite side of the Earth). Assume that you had the capacity to deal with the claustraphobia and the heat.
You still couldn't do it.
Sure, you could make it to the Earth's core, it's centre. That'd be no problem. But after that, it's an uphill battle so to speak. Once you began the second half of the journey, you'd then have to deal with gravitaional forces working against you. You'd be digging above your head.
So you still couldn't do it.
Unless you were wearing some type of jet-pack.
If you're planning such a feat, this is something you should be aware of. Just giving the bad news to you straight.