Some bamboo have a weeping habit and there is nothing you can do about it if you don't like that look. What I can tell you is that pruning bamboo is not like pruning other plants, trees, or bushes. What you prune out is gone forever and nothing will grow back to replace it. As a result, "corrective" pruning that might work with other plants will not work with bamboo. The only thing I have found that will work with wayward culms is to tie them in an upright position until they harden off. However, this works better with large-culmed bamboo where the culm is simply growing at an awkward angle. With something as flexible and thin as what you have, you may not be able to get much benefit from this approach.