If you washed off your cup before placing it there, it’s probably fine. Silicone is pretty resilient. I would still suggest washing it off again and then storing it in a dry place.
If it was left under anti-bacterial soap, and the soap was constantly dripping on it, check that the silicone doesn’t have any signs of deterioration. It may have some pitting or feel tacky/sticky/gummy to the touch which will not wash off. In this case, I would replace the cup.
My daughter leaves hers in the shower all the time, but then again…she uses it almost every day for stress incontinence issues at work.