Guāng shì dàoqiàn shì bùgòu de, nǐ bìxū cǎiqǔ xíngdòng.
Just apologizing is not enough — you must take action.
Tips
grammar
光是 is used at the start of a clause to emphasize that a single thing/factor is already significant or sufficient on its own. It is often followed by 就 (then/already): 光是…就… = 'just...already...'.
