ママの男が部下連れてやってきたわ。
こんな日にシフト入れちまったわ
The characters are two hostess talking in the back room. Host 1 points out mama's man bought subordinates to which host 2 points out she ended up placing her shift in a day like this.
What nuance does ちまった provide here? Is it mean to sound like a complain? Like "oops, of all days I hate pick this one?"
(-て)しまう has two forms of contraction. See also this chart.
ちゃう is generally safe in informal conversation. On the other hand, ちまう is rough and masculine, and it's typically used by users of 俺, ぜ, やがる, etc.
You may translate こんな日に as "of all days", but ちまった by itself is just a rough version of てしまった, and does not have such an additional nuance.
…ちまった (and its source …てしまった) definitely indicates worry/regret about what has happened.
