205 Daytona 650

Hi all
I've just bought a great bike But I think I have been a complete idiot.. I locally bought a 2005 Daytona 650 with 12k on the clock. I was sold to me with a problem, an electrical issue, it wouldn't charge and when the fan kicked in the clocks would die. I didn't think it would be to bad to sort out as although I'm not an auto electrician or mechanic I'm actually a domestic electrician and plumber so quite handy. The previous owner took it to a Garage and they replaced the regulator/rectifier and bypassed the alarm as he thought that was the cause but it was not.
After a bit of research I replaced the Stator, it was completely shot... And now its charging fine with 14+ volts while running.
All good so I thought, but while I changed the Stator some oil came out of the crankcase as expected.
The problem is I replaced about a litre of oil as that is what I thought needed to be replaced, it was a bit low on the dipstick but I thought a quick test ride wouldn't do any harm as I was going for a full oil change next week and didn't want to spend £40 for 4 ltrs at Halfords. (why cant they sell it in 2ltrs?? it's either 1 or 4.) Any way I went out for about 5 miles everything fine, then a mile from home I noticed it wasn't quite running right, a bit difficult to explain, a bit rattly and not as meaty??
Just after I noticed that, the engine management light came on, I rode it slowly home for abut a mile then switched it off, when I switched the ignition back on, but did not start it and now it says low oil..
The question is have I killed my engine does anyone know the best or worse case scenario I can expect or what to do next to avoid any damage.
Many thanks
Matt

 

As I'm new to this bike im not sure of the minimum level, it It was just showing on the dipstick like about 2 mill