It looks fine. If it is puckering too much, a stabilizer will help or even starch. I starch my background squares very stiff before I start.
If it is possible, I also like to cut my background square larger than I want it to be when it is finished. I square it to size after the applique. That helps you fudge things a little if one side pulls up a bit more than the other.
If I were doing it, the petals would be placed behind the center. I would then not do pink stitching at the base of the petal. The yellow stitching around the center would old both. That is a design decision -- not a mistake, so don't feel I'm saying you did it wrong. I'm just trying to answer your questions about what I would do.