You should be able to fill at least same amount as drained.
Since this is first time may I recommend: When you think you are done go for a short drive and let all cool then check the level again on flat surface.
As already said: Start engine, go into all gears letting them engage, then into Park engine running check level and top up if needed - job done.
Out of interest was there any metal filings on the magnet?
Did you stick in a bit of Lucas Stops Slip and which ATF fluid did you use?
Really should have RAVE handy when performing tasks not 100% sure of, sensitive beasts they are
Rave:From 99MY
Refill
7. Refill gearbox to bottom of filler/level plug hole
with correct grade of fluid.
8. Ensure gear lever in the ’P’ position, start engine
and move selector lever through all gear
positions and back to ’P’ position.
9. With the engine idling, continue filling gearbox
until a small thread of fluid runs from filler/level
orifice.
10. Refit filler/level plug using a new sealing washer
and tighten to 30 Nm (22 lbf.ft).
11. Lower vehicle.
