Hi Jenny and thanks for your question and picture of your rubus  plant. The flower doesn't look quite right for Rubus flagellaris, as the petals are rather pointed and the dewberry should be rounder. That being said, the leaves don't look quite right for any of the 3 main blackberries here: Himalayan, Trailing or Evergreen/Cutleaf. I'd say wait for a berry and that will be a better clue!