I have been in your same shoes man. The key to anything in life, especially psychedelic therapy, is ACCEPTANCE.
You being nervous about this is totally normal and in my opinion will not affect the trip in the slightest. Nerves are a normal part of experiencing anything we are apprehensive about. The thing that CAN affect your trip is the acceptance of the changes that will occur during the trip. You may begin to experience apprehension, anxiety and nerves but just accept this as a normal part of your trip and realise that nothing bad can happen to you.
You are perfectly safe, you haven't overdosed, you won't lose your mind permanently, you are perfectly safe. Remember this.
You have to allow all that will occur, the realisations and thoughts and feelings. You might need to cry. This is all good, simply accept and observe whatever happens. Lie down, relax, enjoy the experience. Look into meditation. Get into a calm state of mind beforehand.
You are choosing to do this, you have chosen to ingest this substance and you are doing it for the right reasons. I always felt that the only people who will be bitten in the ass by tripping are either don't accept what is happening to them (freaking out, thinking things such as "Oh my god, this feels weird, what if I dont come back, what if this is permanent, what have I done?" which are merely the result of out egotistical constructs and hold no basis in reality if you accept it as such) or those who abuse the psychedelics for no reason (to get fucked up).
You will be in a good mindset because you will have meditated prior and have a solid reason for taking the psychedelic. This takes care of "set". Look into entheogenic spiritual use of psychedelics and read up a bit, this will inspire your confidence in utilising them as a perfectly reasonable, effective and safe tool for inner exploration.
You will be at home alone or with your girlfriend (I actually prefer being in the woods/nature) and comfortable in your setting, so this takes care of "setting".
Keep positive, read up, meditate, enjoy. You may experience some unsettling feelings and emotions but you will be more empowered and stronger for it. I like the analogy of comparing this experience to weight training and tearing muscle fibres which break down initially and are rebuilt stronger and harder.