Kara, things like that in shops happen, and especially at this time of year when you NEED to get things done and things take longer than expected! Nothing you can do about it!
We are heading into the same territory, thought I'd share! DS is down to 11 - 11.5 hours of nightsleep, which is totally fine, but he's cutting his naps to 1.5 hours instead of his usual 2 - 2.5. On days when they were OT naps he would always make up for them at night with 12 - 13 hours of nightsleep but this week he has not been. After 3 days it is heading into OT territory, and I am juggling ideas in my mind on how to get around it!
One other thing that I thought of in the middle of the night, (as I was desperately begging DS to get back to sleep at 330 am

) is that we went through something like this at 8/9 months old. Stick with me while I explain this as I might not say it clearly. You know how LOs will often wake early because they are not getting enough A time before their nap and/or are napping for too long early on...so they wake up earlier in order to get the A time they need? Well, when DS was 8/9 ish months, he started doing the opposite -- cutting his nap early in order to get the longer A time that he wanted/needed in before bed. Basically he needed 3.5 hours before bed and the only way to get it was to wake himself by 3pm because his body clock was set on a 630 bedtime. No matter if he only went down for his nap at 2pm. I was desperately trying to get him to nap later so he could do to bed later, but he was fighting me by waking up by 3 because he knew instinctually that he had to go to bed at 630. Am I explaining this well enough?
By the time we realised this I felt pretty stupid. And then it was back to the age old question of how to push the A time on the short nap, kwim? I just started pushing his bedtime gently, 10-15 minutes of extra A time and kept the ENTIRE afternoon after his nap as calm as possible, not just the end bit, so that he got used to the fact that he was being kept up later....and yes, his naps started stretching out later to make up for it. I really wish that I had brought all of my old EASY notebooks with me when we moved but that just seemed even more absurd than the fact that I actually had them in the first place!! But, I am thinking that is what we are going to need to do now. So for instance he naps from 12 - 130, a 1.5 hour nap means he can only last 4.5 hours so he is in bed by 6pm. But he just will NOT nap later than 130 because his body knows he is going to bed at 600. So in order to beat this I am thinking I need to gently push him to 615 for a few days but keep the rest of his day the same, and try to get an extra 15 minutes out of his nap. And then the same a few days later.
Does that make sense? (As in, do you think I am crazy??!!!) I am not sure if it will work with one nap the same way as it did when he was younger and on 2 good length naps ....