You can try practising at night even without kakis, after 9pm when the traffic is lighter. Take your bike and ride around your place. Once you are confident, you can head out to the expressway. Ride at a comfortable speed. You don't have to hit 90km/h. Even 60km/h is fine. Just keep to the slowest lane until you are confident to up your speed. 2B bikes can be wobbly at high speeds, so take your time.
And remember to always always wear a fullface helmet, gloves, a riding jacket and proper shoes.