Eep!
Honestly, you've got two choices really;
1) Any Damage is theoretically already done, so just pretend it didn't happen and carry on driving it until you get a problem :lol:
2) Cam covers off and check for evidence of damage (broken valve springs/valve/follower spacing out of tolerance/loose/damaged followers indicating bent valves), whip the spark plugs out and check for any valve/piston contact with a borescope (if the valve springs didn't close the valves fast enough at whatever peak rpm you reached), and finally pull the sump off and check the bottom end bearings. Unless you do a full engine teardown you'll never know if you've stretched/damaged the rods - the forces due to acceleration/deceleration of the pistons at whatever speed your engine will have reached will be pretty significant, but perhaps unlikely to have resulted in damage for the fraction of a second you buzzed it, but nothing is guaranteed...
Good luck with it, that's rough luck
If it's any consolation I had an old Peugeot 306 GTi6 and did exactly the same thing as you; went to top of 4th gear (7.3krpm) went for 5th, accidentally got 3rd, rev counter went off the clock past 9 for a good few seconds before I realised. Car ran absolutely fine, did another 20k miles before I sold it on :lol: