They are called hose clamps. I hope you used stainless steel ones. You can cut the extra part with tin snips. File or grind away the sharp edge, and when you cut it, it will leave a sharp edge. I'm not quite sure if you can reuse them if you take them off after cutting them. So have extras.
You can also try to find ones that have a plastic cap thet goes over the end, of paint on some plastic-dip, made to coat tool handles. They will hold the water bottle fine.