Dahlias not fully opening

First time total newbie and failing a LOT. I finally got some buds that started to bloom but it’s been weeks and they haven’t fully opened. These are also super super tiny, like 1-1.5” diameter. We’ve had tons of rain, humidity, and 90+ degree days this summer (7a) and I lost half of all the dahlias I planted to stem rot (see additional photos). I had one bloom that looked great but after 2 days of rain the petals turned brown and it started rotting 😭😭😭 I’m so freaking sad I’ve spent so much money and time and effort trying to grow dahlias and it’s September and zero successful flowers. Most of the tubers were from Eden Brothers and Plantgem.

by brienneofbark