Why is the cyclic voltammetry of my ferrocene compound not showing a standard shape?

I am trying to set-up a new cyclic voltammetry measurement station in my lab but the results are very poor. I am using the following parameters:

working electrode: platinum wire, 0.25mm diametercounter electrode: platinum wire, 0.25mm diameterreference electrode: nonesolvent: acetonitrileelectrolyte: ferrocenecarboxaldehydesupport electrolyte: tetrabutylammonium hexafluorophosphatescan rate: ~600mV/s

Platinum wires each have a submerged length of about 2mm to 5mm and are separated by about 2cm. I was previously using tetrabutylammonium iodide, but that is probably not a good support because the iodide ions will become iodine and forming a blocking layer on my electrode?

I also tried using graphite rods as the electrodes but obtained similar poor-looking CV shapes.

What should I change to obtain the standard CV shape of an outer-sphere redox species?