Sounds like they were pretty harsh if they totally failed you for doing just that wrong. But.....as has already been said, you will NOT forget that stuff again! The real world is so much different. So long as you are not forgetting anything crucial, nobody is going to say anything to you. You can also choose not to do certain techniques. Heavens to betsy, if I used every technique I learned in my massages, I'd never be done in 60 minutes, or if I did, the massage would be so fast, it would be invigorating instead of relaxing. Of course, there are certain things, that if you do them wrong are going to be detrimental. If you are using poor body mechanics, you are not going to last long in the profession without lots of aches and pains. If you forget to work superficial to deep and you are always working too deeply too fast, your clients are going to be uncomfortable and most likely not come back. If you are working directly on bone, the client is going to be very uncomfortable too. You get the idea.
But, if you don't ask about the pressure as often as the instructor thinks you should or you don't do a "good-bye" stroke on the arms, you are not going to cause any harm or ruin a session and nobody is going to notice.
Sounds like you have a very good attitude about it and are learning from the experience. Way to go!