Gaps in print around walls

[JessJ 0]

Hi all. I'm sure I'm missing something basic here and I've tried playing with settings as described on various troubleshooting guides but I'm at a loss so I've come here x

 

I seem to have a gap between walls and the main body of the print. I first assumed it to be not enough top layers but this is 90% gyroid infill and 12 top layers. Holding the print up to the light shows that there only seems to be a bottom layer where the gaps are. I'm sure I am missing a setting, I just can't work out out what it is.