Hmmm, while I can't say I've really been there, I will say that that is exactly why I'm trying to do this as laid-back as possible.
I do not have a wedding party, I did not send STDs or official invites (I let our parents on both sides let anyone in the family who wanted to come know about the wedding...it's basically an open-invitation to family, the more the merrier but no bigee if they can't). I'm not doing OOT bags as half of the people attending have already been to Mexico and know what to expect and those who haven't probably have a good idea.
I think why I'm doing it this way is part laziness (I'll admit I'm not the biggest DYIer out there, though I love what many of the ladies on BDW do for their weddings, good on em for having that kind of motivation!! ) and part trying to make this as cost-effective as possible. I have essentially made all the decisions that matter in regards to the wedding location/date/time/food/etc, and the FI just gives it his obligatory blessing haha.
I'm sorry to hear you're stressed, if I lived in Calgary, I would totally offer to help you out! I hope everything turns out for you!