Yes, you are right. Currently, the browser keeps track of whether you’ve spun the wheel, so if you clear your cache or open the page in incognito mode, you actually can spin again.
Unfortunately, it’s impossible to change this behavior now, I am really sorry 
However, the good thing is that the form feature is going to be rolled out quite soon, which will allow you to collect participants’ emails before they spin. This way, you’ll have better tracking in place.
Additionally, I’ve added a request to the Wishlist on your behalf for limiting the spins per IP - Ability to limit spins per IP address