I am happy to be involved in extra-curricular activities as long as there is an opportunity to rehearse and work things up, rather than just hanging on by the skin of my teeth.

--- I'm not sure what in the context of this sentence this phrase means???
I thinkg it means that this person doesn't want to be involved in other activities if that means that the person will be just getting by, without time to reahearse, etc.
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I understand. Thank you!
"skin of my teeth" is a metaphor. It doesn't work very well in your sentence. "Hanging on by my fingernails" would be better.
"I was surviving by the skin of my teeth," means surviving by the thinest of margins, the skin of one's teeth being very thin--non-existent actually.