My son is 5mo and I have been dealing with this same problem myself since he was about 2mo. Even when he naps in his crib I still find myself tensely waiting the whole time to see if he will wake early or have a good nap and I am so afraid of messing up all the hard work we have done that I overthink every daytime decision...what if he falls asleep in the carseat? Oh no!
Recently, through a lot of help from other moms I have realized that the routine is no good if mommy is crazy because of it! For us, the goal is to have naps in the crib on a regular basis but life has to happen and mommy needs out of the house sometimes and bad naps will happen no matter how vigilant we are so if you have somewhere you would like to or need to go, then go. It may throw her off for a day and it may not but a happy mom who feels like she has a life is more able to deal with a bad nap than one who obsesses over the routine (like I did for 3.5 mos).
In fact, what I have found is that little deviations from the routine are much more traumatic for me than for my son (the worrying about what will happen versus being a little bit cranky for him). If fact, the more I am flexible and allow life to happen the more I relax and I think my lo responds to my more relaxed state and rolls with it himself.
Your concern shows that you are a great mom doing a great job.