I got caught red handed

So long story short, my parents went out to California for a week and my neighbors told them that a car (my boyfriend's) was there when she left for Sunday School at 7am (which I totally forgot about and thought that he'd leave before they woke up). I've already apologized but they are still furious at me for lying to them (which yes I know is wrong but I rarely have any alone time with my boyfriend). I know being proactive in handling my punishment of the situation softens the blow immensely but I just don't have any ideas. Can anyone give me some advice?