Finn adds " if you can" rather than 'if possible' to his special request so that he sounds polite when asking for an urgent appointment - he wants to see the dentist at very short notice.
Finn在提出了特殊要求之后,加上了If you can(假如你可以的话)而不是if possible(尽可能),这样的话,他这种紧急情况下的紧急预约听起来就会显得很有礼——他要医生要得很急。