Then I fear blaming Christianity is a bit weak. I get that you are annoyed. I might be too if I could be convinced to exercise. I think you are hitting this annoyance nail with too big a hammer. Because the fact that a week consists of seven days is also due to the influence of Christianity. And even in sensible the-week-starts-on-Monday-Europe wall calendars on sale often list Sundays first. Your mobile phone probably has a setting for that as well. Take it as a lesson learned and let it go.