[Gumlegs]

It really depends on whether you're writing "natural-sounding dialogue," or you need show correct usage. "Half-bad" is the way people talk. "Half-badly" is correct English. "Half-badly" is modifying "day," telling you how the day went -- badly.

"The day went bad" would imply that, perhaps, the day joined a criminal gang, or had been kept past its expiration date.

The correct possessive is Parks's, by the way. (The possessive "Jesus'" is an exception to the rule).

[Gumlegs]

No, it's not. It's modifying "went." What a moron. (It should still be "badly," though).

[Dog Gone]

The correct possessive is Parks's, by the way.

LOL. That was the first thing I noticed, and I was beginning to doubt whether anyone would ever mention it.