Paul,
Looking at your photos with envy - it’s many years since I’ve sailed my boat off Corfu.
As others have said, there will always be a certain amount of gapping on the now vintage and highly collectible gunter-rigged BR20’s such as yours and mine. However, the gap could be a little reduced in at least two ways:
1. From the photo that you have posted, it looks like you have the downhaul arrangement that came with the boat when new, which can be difficult to tighten sufficiently. I have replaced mine with a downhaul with a bit more mechanical advantage, as in the first two attached photos. To tighten you pull the downhaul down rather than upwards, as in your original arrangement. By the way, I'd replace the hardware that attaches to your luff's bottom cringle with an open hook like mine in the second photo - it's much quicker to attach than a shackle, which is important when reefing.
2. I don't know how things work with a square mast compared to a rounded one like mine but I'd normally replace the thin strops you have around your mast with a stouter parrel bead and loop arrangement which allows you to adjust the tension with which the luff is held against the mast. See the third photo. I don’t think I’d ever be brave enough to forgo the strops, as Andrew suggests.
If your carbon fibre gunter yard is on the soft side, as many of the original ones were, you’ll find that the top of the mainsail sags to leeward in any sort of wind. It may also sag backwards when you tighten the downhaul and outhaul. None of this is helpful to efficient sail trim! If this is the case, it may be a good idea to replace it with something stiffer, as in this thread
https://www.swallowyachtsassociation.org/smf/index.php/topic,2923.msg16636.html#msg16636. You might find a good secondhand windsurfer mast at the end of the season at Avlaki.
