As it is the St. Valentine season you complete a level you get × amount of roses. Once you have collected enough roses you exchange them for a certain item, according to the worth of the roses. I had collected 2660 roses waiting to earn just 10 more to get the last item on the list but I was struggling with the level I was on. Eventually when I finally completed that level I realized that all my rose were gone and I did check, no I did not accidentally buy anything with those roses, they're gone