[Measurement Check] currently wearing 36D, when I swoop and scoop the cups are overflowing but within an hour have gaps

Hello!

I have been wearing a 36D for ages and I know the fit isn't right because the cups feel both too small and too big at the same time. As stated in the title, when I scoop my breasts into the cups, they always overflow out the top but after awhile, when I look down, there are gaps along the top of my bra. Tightening the band helps, but hurts for long term wear.

I did my calculations both in inches and centimeters (not sure what would be better) and received size 36E/F in centimeters, and 36F/FF in inches. Measurements below

Loose underbust: 94 cm/ 37 in Snug underbust: 92 cm/ 36 in Tight underbust: 87 cm/ 33 in Standing bust: 106 cm/ 42 in Leaning bust: 112 cm/ 44 in Lying bust: 106 cm/ 42 in

As far as I can tell, my shape is slightly bottom full, centre full, and I think splayed.

Thanks!!