Hi JPN18,
Welcome to Affinity Forums
To check the DPI value of your document in Affinity Photo go to menu Document ▸ Resize (dpi field). Currently there's a bug when exporting files that prevents this dpi value from being written to the file if there was already a previous/existing dpi value in the metadata of the image/file. To work around this click the More button in the export dialog and untick Embed metadata. To confirm the dpi value of the exported file open it in Apple Preview go to menu Tools ▸ Show Inspector. The Info tab (on top) of the Inspector should list the dpi value.
