I think the clock restarted when you left for the UK:


Transit under the Visa Waiver Program

Travelers who qualify for visa free travel under the Visa Waiver Program may transit the United States. Prior to boarding the carrier they must obtain travel authorization under ESTA.

If transiting the United States to a destination in Canada, Mexico or the adjacent islands, the traveler may re-enter the United States on the return journey using any mode of transport, as long as the total visit, including both periods of time spent in transit and in Canada, Mexico or the adjacent islands, does not exceed 90 days. If transiting to a destination outside of Canada, Mexico or the adjacent islands, the return journey must be on a participating carrier, but need not be within 90 days, as the traveler will be required to make a new application for admission.

http://london.usembassy.gov/niv/vwpnewcountries2.html


But they might worry that you're actually planning to try to come live here (though this is probably less of a concern for someone from the UK than other countries in the world). Being a young university student, if you are, would help you. But if you want to worry, you could bring a copy of your lease or proof or student enrollment/job info, if you'd like.
I'd be surprised if you got much trouble, though.

I wouldn't worry about your friends coming to pick you up; I'd doubt this would raise an eyebrow. LAX is cool enough people like to go there.

And I think black friday is totally worth it, especially since you won't be trying to get the great deal on the big screen TV and won't be worried about not getting it. It's an eye-opening experience.