Pastel is generally a 'messy' medium to use, and with normal sketch paper, it will pose a few problems. I myself have had this problem before, and would suggest trying to use pastel on velour paper, which is available to order online. You will first have to draw a pencil outline and then use the pastel. With velour paper, you won't have to put in as much effort and with light strokes, you'll be able to give the flower a softer look with no blending, due to the paper quality.
I have attached an image of one of my velour paper pastel drawings below:
I hope this helps and do not hesitate to ask me any questions.