Hi all, I built this bow and when shooting, the arrow goes straight for a few feet and then flies upward. I'm using Thera-Band black tubing. I'm using Carbon Express fiberglass arrows 26" and 28". These arrows are too heavy for some bows but shouldn't be a problem with this slingbow. I've also used a very lightweight dowel arrow with the same results. Does anyone know what the problem might be? I later even added a whisker biscuit (not pictured) as an arrow guide, but the result was the same.