Kieth
This is perfectly normal.
Same thing happens on my 36 in light winds and can be overcome with a tug on the boom normally as learnt from my dinghy sailing days.
Alternatively you could slacken them off a bit so they are not under as much tension and that should stop them going into the s shape however I prefer to keep tension on mine as it improves the sail shape and airflow across the sail.
Regards
Rick
