Recall that the Scapular is like a religious habit. If a monk would take off his habit to, say, take a shower, or do some kind of work that cannot be done safely while wearing a habit, without therefore being said to no longer be a religious of that order, then you can do the same with a scapular.
Scapular is not a magic talisman, and God is not waiting behind a bush to strike you dead the instant you take it off for a shower.
Wearing the scapular means that you should HABITUALLY wear it. Habitually wearing it does not mean wearing it every moment of every day, but that it's part of your regular clothing. So, for instance, pretty much every time I get changed or dressed, I make sure I put the scapular on just before putting on my T-shirt. In other words, it's as regular a part of my wardrobe as my T-shirt is.
Trust in God's Mercy. If you wear it regularly, have confidence that he will not cut you down in the shower if you happen to be in a state of sin and for a few minutes remove the scapular. That is not God.