Yup, I've been doing this since the feature was implemented in beta... when you say it tells you "wake not scanned" that sounds like something it says when you try to jump with a wake selected when you are NOT in supercruise, and either haven't scanned the wake(or don't even have a wake scanner). You ONLY need a wake scanner for wakes when you want to follow them from regular non-supercruise mode. if someone jumps to another system you can follow them that way if you have a scanner. But If you are already in supercruise, you don't need a scanner. It takes a bit of time to get a handle on just what is happening when you accelerate-decellerate in supercruise. I think it's possible you are overshooting because you're not decelerating enough at the right time. when the wake switches from being 0.1LS away to 25,000 kms, you need to already be down to about 4,000km/s
In supercruise don't think of the throttle as setting your speed, it's actually adjusting the time-to-target, with the center of the blue being about 8-10 seconds. As soon as you reach the 8 sec-to-target distance, you should lower your throttle to just below the center of the blue area on the throttle and try not to let the distance close closer than 8 sec until you are about 7000kms away.
Forgive me if you know all this, it's not super-obvious and there are a lot of new people playing now that can probably benefit to hear it.
After a while it becomes second nature, and you can pop into wakes really quickly, but it's just as hard to find the balance as it is mastering fast/safe docking

so not THAT hard with a bit of muscle memory.
I finnally managed to jump into my friends wake, once you know how to do it, its really easy indead, still by reading it here i found it still horrible hard to comprehend at first.
Not to point fingers or trying to undermine/insult any of you, i think most here try to explain it too overcomplicated, since the procedure is relative easy.
My n00b guide for this is..
Select the wake you want to jump into from Super-Cruise (you'r friends for example), look at the menu on the left with the 2 bars in it. (same one you use to look at for USS, Stations etc etc so you dont overshoot them).
Then when the both sliders hit the Blue part of both bars, you get the Safe to Disengage popup, press J and violla your in the USS of the one your following.
Its exact the same procedure as you use to get out of SuperCruise for an station etc, only difference is, in the HUD itself it doesnt show any distance or whatever, just the wake icon.
At least thanks for this thread it woudnt had it figured it out, i started out at launch of the game a couple of days ago, and first glance i was stunned in how bad Coop'ing was done, i just coudnt figure out how to join my friend(s) their USS. so after some much reading, including this thread, i allmost yelled this game really sucks balls, but then somehow suddenly i noticed that left menu that it was responding as well, only due the "lack" of indicator of distance in the HUD itself like you have with normal targets what i assume most people use at first guidance, that they like me, forget to look close to the left side menu, and complete overshoot the wake.
Now that i have figured it out, the game became suddenly ALOT (cant emphase this enough) ALOT more fun to play

All we have to hope for more contents for the long run, like coop missions more stuff to grind for etc, the core game is there, and its really good, but it does seems lacking in contents, and becomes after a few days just a grind for getting a bigger ship so you can grind more for a other ship thats better as previous. on short term thinking its ok, but on the long run this is just too boring.