Hard to judge at this size, but part does seem to be in focus, but it looks like this shot is setup such that any non-macro lens would have issues. You are presumably, very close to MFD (minimum focus distance), which is 11" from sensor. Non-Macro lenses are NOT optimized for this. I would expect softness.
I'm not sure what settings you were shooting at, but assuming 50mm, f/2.8, with the flower near the minimum focus distance, your DOF is tiny... DOFMaster says it's about 0.1", roughly 0.05" in front and back will be in focus. Typically DOF is calculated for what would make a good 8x10 print at 100dpi, but we're all much pickier than that. Viewing zoomed in on a monitor, you will see blur at much less than 0.1". This is probably the worst-case shooting situation you could create, for any lens.
If you want to be shooting flowers, and other small things, I'd recommend you return this lens and get a macro lens. If this isn't what you want to shoot, then I suggest re-testing the lens on a subject that's more typical of what you want to shoot.