You're not doing anything wrong. Really, as long as you're being sensible, there's no right or wrong way to do a wbtb.

Try adjusting your alarm a bit, do some experimenting, soon you'll find a time that works for you.

Also, if you have a traditional alarm sound, maybe switch it out for something that will wake you up more gently.

Good luck

(cheer up and stay positive. they will always fail if you think they do)