I have been prescribed ropinirole for rls. I was wondering if I could take an over-the-counter sleep aid as well?

No. Many over the counter sleep medications contain antihistamines which commonly worsen RLS symptoms. I would follow-up with your physician to make sure you're on an effective dose and have ruled out other sleep disorders, such as obstructive sleep apnea and insomnia.
Not Good Idea. Many over the counter sleeping aids that contain antihistamines w/ Diphenhydramine (benadryl) in them like tylenol (acetaminophen) pm, or advil pm or antihistamine doxylamine as in unisom make RLS worse. Melatonin may actually worsen symptoms too. Talk to your doctor about getting help in sleep; evaluation is important. For now be careful you aren't taking something that may turn out to be a restless leg trigger.