Having reached Red belt, more is expected of your Bassai-dai ability. Therefore it’s important to practise regularly at home (and even before and/or after class).
Your overall ability must have improved in the kata, with less tolerance of bad habits or neglect in the finer details. There is no point being fast or explosive if you have poor technical habits as these will not serve you well in self-defence.
When practising, go through the kata in super slow motion. Going through in super slow motion enables you to really think about each and every aspect of each movement. It allows you to ensure you are performing it 100% correctly, creating muscle memory and positive habits.
It also allows you to identify poor habits (and correct them), habits that you may not have identified at regular pace. Going at this pace also means you wont pull any muscles or work up a sweat (so you can even practise at work in your office).
Once you have practised it a few times in super slow motion, build it up to medium pace and then finally at regular pace.