Hi Emily,
Please tell me which training plan, which week of the training plan and which exact day you are asking about? There is not a workout in our LW Coaching beginner training plan that recommends targeting a specific wattage. The beginner training plan does not have test sets. The beginner training plan is focused on skills, consistency, strength and cadence, not power. I am very curious where you got this from. Please specify.
300 watts for 20 minutes is a high power output. This is above the lifetime best power of most pro women. No doubt you found it incredibly difficult!
Coach Lynda