It's fine for "free at last". For "at last I'm free", just add sum ad the end.I assume you are a woman, right? "Libera tandem", maybe. Wait for other opinions, anyway, maybe they have better options.
That's "at last (I'm) freed".Hi,
I'd say this: Tandem liberata (sum)!
In capital letters: TANDEM LIBERATA (SVM)!
Isn't nunc demum more like "now at last", "only now"?NVNC DEMVM LIBERA