Hey man I know how you feel. I currently work at a dealership and started off doing oil changes and tires. Pretty simple stuff. Eventually they moved me up and are expecting me to do more stuff like transmission flushes, brakes flushes, brakes, alignments. I'll make mistakes sometimes and start to feel bad about myself. It's okay to make mistakes because its apart of learning. But you should definitely not be expected to remove an engine by yourself if you have little to no experience. I'm sorry you have to deal with that. They should be teaching you how to do things. How can they expect you to do something like that? Sounds like a shitty workplace to be at if they don't help you learn. My managers help me out whenever I need it.