Three weeks is a very short time to be expecting so much. Don't worry about it. Remember everyone out on the mat started at the beginning and is still learning. It took me a good 5 or more YEARS to be comfortable with some of my rolls, and I still really hate doing high-falls. Everybody has a different body, and it is certainly easier for some than it is for others. Give yourself time (I know you don't want to hear that, but it really is true) and it will improve.
As to the idea of holding people back; you are not!!!! Beginners are terrific teachers for anyone training who can see it. They don't move where you want them to often, and then the more advanced practioner has to analyse their own technique to make sure it is really being applied properly. I love training with beginners! (I love training with almost everyone for that matter)
Now, heal, and then go train.