You may have been premature with the shorter cranks. It probably is wise and wait until you develop a good base of training time.

However since you lack power, it's good to start working on it. Try some intervals of a minute or two pushing a bigger gear at a cadence of 75 or do. Then relax and recover with an easy gear spinning. For several of these and gradually increase the duration over a period of weeks.

A cadence of 90-100 is good for efficieny but not speed until you learn to combine both through lots of riding. Most people are faster at a cadence of 75-85 but they can't usually keep this up for long durations.

Experiment and see what works for you. Dont try and force some number on your own training