If you are not satisfied with the sharpness, consider a few suggestions.

You may have had several gremlins conspiring against you. You use a 70mm focal lengh at f/4 which, especially at close distances, yields a shallow depth of field. This is not necessarily a bad thing- the softness is nice IF HOWEVER, there is one sharp element that such as in the detail at the center of the flower. I don't think you have camera movement blur but it is hard to difficult to maintain critical focus at wide apertures, longer focal lengths, and close distances. A tripod or monopod would help.

ISO 800 should not seriously affect IQ- perhaps just a bit more noise but I don't think that is your issue with this image.

In my commercial work, I do lots of flowers- that is because I do work for the Canadian Florists association and several horticultural organizations.

So, keep the camera steady with support equipment, decide on the depth of field issues and open up or stop down accordingly, sometimes manual focus works better, and try to give the viewers' eye something relatively sharp to become the point of interest.

Natural light is my favorite for flowers in the natural environment. - I only use flash occasionally on studio shots of floral arrangements. Try back ligh that trans-illuminates the leaves or petals.