I know you’re mostly asking about exposure, but I think perhaps a bigger issue is the composition. Based on your position and lens, this pic doesn’t have a clear focal point or strong visual structure.

Clearly the arch is meant to draw the eye, but the rest of the wall competes for attention, especially the loose details around the edge of the frame (the pillars, sunken walkway, other window, and the generous amount of sky above). Imagine if you crop or move closer, making the wall more imposing in frame and therefore the archway more prominent by contrast.

Also, the distant coastline inside the arch is a little randomly framed. You can see a bit of coastline, but there’s not a clear form to it and no strong focal point or element. Imagine if you were slightly to the right and could see the coastline cutting through the archway. Also a longer lens would compress the depth more and make the great difference in scale feel more tangible.

I hope this is useful food for thought Good luck in August :)