(1) Ch 4 + sl st and work in the hole not the stitches, or (2) google Magic Loop, or (3) ch 3 and work into the first ch.
For (1) and (2) ch 2 instead of first tc. (3) you've already done it. That's your starting shell.
#Ch 1, 3tc (shell)# 7 times. Ch 1, sl st to join
Starting shell, ch 1, shell in first gap. $Ch1, shell in next gap. #ch 1, shell# twice in next space$ twice. Ch 1, shell, ch 1, sl st to join.
That's the first two rounds. Each round has a greater number of single shells between the doubles. As long as you do 2 shell between each pair on the previous row, you'll get corners.
Rows are also good. The edges will be hidden by the joining and edging processes, so don't show :)
You can do this