I don't have a quick fix for the Velcro closure. See if any gunk has clogged the sticky part and try to situate yourself so that you are on a slight diagonal. I usually hang the foot end just a bit higher than the head end and rarely have had a problem in over 10 years of using Hennessy Hammocks.
BTW, you could use an Explorer model at your height. The Explorer Deluxe weight range is OK, or the Explorer UL with a rope upgrade would be within warranty specs. Also, an Deep Jungle XL would work for your height and weight. You might consider one of these to reduce pack weight and volume in the future.
Hennessy Hammock afficionado and supporter.