Its definatly too soon to get worried.. Anenomes deflate and retract for a number of different reasons. Some being that it has just eatin or that its about to expel waste. Or it just might want too, unless it gives you some other indication of there being something wrong IMO I would just observe it for now. I cannot tell from your pic but what size tank is it in and what type of lighting do you have? Although 20ppm of trates is tolerable for an anenome its not healthy long term. Achieving the lowest PPM of trates should be a goal. Is it still eating? If you could provide some more information it would help to figure out what could be wrong if anything.