Driving school motorcycle often tilts while stopping

I hope you can give me a little bit of courage and maybe give me some tips. I have 13 driving hours so far and my instructor wants to take the test with me next week Thursday. Everything really works great (start, turn, bends, I have all the basic driving tasks on it), except that stop for example at a crossroads. As soon as I get to the intersection and stop brake I will become incredibly unstable I can still catch it, but it still feels very funny and unsettled. My instructor only says “when braking or stopping, always keep the handlebar straight”. I always talk about that before the crossing, but it doesn’t work that I get to a clean stop. I hope you’re someone who can give me some tips on how to somehow get this cramped stop. A lot of things to do. Thank you very much! MfG Marc