I Pooped My Panties On A Trip

I was part of a group that was visiting old ruins in mexico.  I was in high school, and it was a special perk for seniors who had done well in science.  We were out for most of the day, and I went #1 whenever I needed, but didn't want to go #2 because the "facilities" had no TP in them, and ... I just didn't.  But I had to go a lot and when were were walking down a long hill from off one of the sites it just got more and more urgent.  Then it just came out.  A very large fairly hard poo.  I was wearing a short skirt and cotton briefs underneath.  It filled my panties and I didn't say anything.  We were outside, and I think nobody noticed at that time.  I walked around like that for about 45 minutes, until we almost got back to the bus.  It actually didn't smell at all, as far as I could tell, but then the group was outside.  I stayed behind, at the back of the group and didn't say much.  Finally one guy came back to talk to me after a bit, when we were almost back to the bus, and asked me if everything was OK, since I seemed kind of withdrawn.  I didn't know what to say, and I started to cry.  He asked me what was wrong and I said nothing, but I just cried more.  He stayed with me and tried to make me feel better, and then suddenly, I don't know how, but he realized what I had done.  His face got red and he said he was sorry.  I just kept sobbing, and other people in the group noticed.  I couldn't say what I had done.  I didn't say anything, just kept sobbing.  Finally he said "Diane pooped her pants".  I thought I was going to die of shame.  People didn't know what to say.  Now we were at the bus.  I finally went behind the bus after everyone else was on it, and emptied out my panties.  But they were badly soiled, and so was my behind.  I came onto the bus and sat by myself near the front.  Now I noticed the smell.  I am sure that others did too.  We didn't go to the last stop because of me, but went back to the hotel, where I went to my room and changed and showered.  I had two more days before the trip ended and we returned home.  I was too ashamed to look at anyone.