Worried about layover, Heathrow - Dallas/Fort Worth - Mexico City

I have been a bit impulsive and booked my first solo trip, going to Mexico City from the UK for 2 weeks. I bought tickets through BA, but flying with AA, so if this isn't technically an AA question call me an idiot and send me on my way.

I am travelling from Heathrow and then stopping in Dallas/Fort Worth for 1hr 36 minutes, how fucked am I? I didn't realise I needed to go through security again and now am a bit worried about how tight it'll be. From what I've seen I need to go through customs, get my bag, send my bag back on it's way and then go through security again? Will I have enough time to do this? And if I miss my plane will I need to just get another ticket or will I be able to sort another flight with AA/BA? I'm just a bit anxious atm and have never done a layover before, so sorry about the ramble!