I've done prolonged exposure therapy for my fear of injections. It was definitely terrifying at first but thankfully my T was helpful. It took us about 3-4 months (out of the year of me seeing T) to get to the point where I can hold an actual needle. However, dont mean to scare you or anything, I began getting really overwhelmed at the last few steps so my T decided it would be best to stop the exposure for now and come back to it later on. It might be really really scary at first, and that's expected. Your T is trained for this kind of stuff and will help guide you through it, and if it gets too much just say that you need a break.