It is often taught that when you are astral traveling and you meet something that scares you, you should send it away, often to "the light," or leave yourself. Things aren't quite that easy in shamanism. Often you will be shown or put through very disturbing experiences. In fact this is often used in initiations or ceremonies in the spirit world to destroy the old and bring in the new.
This goes back to the idea of creation and destruction. Something must be destroyed for something to be created. We all have inner demons to face and facing them is rarely a pretty sight or a fun experience, but it is something that must be done if we wish to change and grow. Most people are uncomfortable with change because it delves into the unknown, but you need to learn to be comfortable with it if you wish to use shamanic practices successfully.
Do not be afraid of what you will face when you travel. Your guide will be there to support and protect you. They will take care of you body and protect you from things not involved with your journey. If you are actually truly uncomfortable and frightened by something you are supposed to face then you are probably not ready to face it. Learn patience and come back to it another time. However do not just ignore it and hope it will go away.
Another bit of advice. Be careful when you travel. Always ask a spirit guide to guard in the physical realm and in the spirit realm while you travel. They are glad to do this, just remember to thank them. Remember that while you are journeying you body might as well be asleep. This means no journeying while bungee jumping or performing surgery or anything else that requires alertness or might entail danger.