Concerta is a time release. It normally lasts for 8 to 10 hours, but with this overdose it will last much longer. The worst should be the initial hit, but you will feel the effects as more of it gets released over time. But, it should not be as bad.
Your note doesn't quite make sense as you said you took it today, but then you said, " I haven't even eaten in the past three days." If you had not taken the overdose untill today, but you have not been able to eat for 3 days then something else is going on.
Make sure you are getting plenty of fluids. A sports drink would be good. If you have not taken the med till today and have not been able to eat for 3 days, then I do think its time to see a doctor, because this is something more then just the overdose you took.
Oh, the max dose for an adult is listed as 72 mgs, but adults do take more without a problem (if they have built up to that level).
Something is obviously going on for you to increase your dose by that much. If you want to talk about it, feel free to message me.
Good luck! hope this helps.