Echoing my YT comment here:
At around 17:30, 121.30 is listed as the final approach frequency, you should be expecting to be sent to that at some point (ie, it would be a indicator that once you're on that freq, that's who is going to issue the app clearance, therefore, it would be reasonable to get the tower freq into stdby once you're on that freq). Later, when the controller issues the freq, you didn't read it back. Reading back numbers is generally considered good practice. It prevents basic miscommunication, and selfishly, simply SAYING it helps the pilot to cement it into short term memory.
Case in point, you didn't read it back, then you needed the replay feature to recall it, and then you didn't enter it correctly. Just like accidents are made of chains of events, so to are mistakes with freq changes. And THOSE can lead to stress and additional workload.
Definitely consider small changes like this to improve your efficiency. I can all but promise that the flights will go smoother and your workload will drop.
Final point, when you dial in a freq, say it out loud. LOOK at the numbers you're dialing, making sure that what you're saying matches what you're dialing. This is a technique that Rod Machado teaches, and he's spot on. It all be removes the possibility of this sort of thing happening. Great video, btw! Please don't take the comment otherwise.