It is essential to practice Keyboard Harmony in multiple RH positions. Once you've learned how to play a passage, the next step is to play it again, starting in a different RH position. The only way to gain true fluency in figured bass is to practice passages in all possible RH positions.
When you find a chord that is really hard to play on time, practice starting the chord before, and stop on the hard chord. Do this maybe 10 times and you’ll have it. This method takes about two minutes. If the next day it reverts, you’ll find it only takes 5 times to get it. And so forth.
There are two different types of practice you must do: Accuracy Practice; and Fluency Practice.
Accuracy Practice: when you make a mistake, you stop and fix the mistake. You repeat the problem passage until it is corrected.
Fluency Practice: when you force yourself to play an entire phrase or a set of phrases from beginning to end without stopping NO MATTER WHAT. This teaches you to shrug off mistakes in the RH. This practice obviously comes after Accuracy Practice.
You MUST practice both ways for this class. Remember that rhythm is an incredibly important element in harmony, and in order to learn it, you must force yourself to play with correct rhythm (at the expense of accurate pitches).