Nope, don't worry about missing one dose. It's totally fine and it happens. You don't need to double up or do anything else, just continue with your normal course of taking it daily and it will be fine.
Don't worry about missing a dose of isotretinoin. It won't hurt you nor will it affect the outcome of your course of therapy. You should speak with your dermatologist regarding this issue to get his or her view on it.