Automatic Trans are generally idiot proof.... RPM's are governed to never go over the recommended RPM's and in your case, it looks like the car was engineered to upshift for you, if you kept a low gear engaged for too long, in "fake" manual mode.

Even real manuals are governed to not go over a certain RPM... but since it's manual the car will hold that gear until you shift it yourself.

So you didn't hurt the car, but you did put a bit of excessive wear on the car. In the same fashion as driving like a race car driver would tear up a car...

If you don't have any problems now chances are all you did was shorten the life of the motor and transmission .

You mean overdrive! No damage to the motor unless it is low on oil and coolant when the engine is stone cold.

It should be fine. I won't share any feelings about you feeling stupid.

So I am a new driver, first car, and was wondering why my rpm was so high. Around 3k and like 5-6k at 35,40mph before it would change gear. Turns out I was driving the car in manual, instead of having the car in drive..... I feel so stupid. I was driving like this for 2 days, quite a few miles. I was wondering what affect this will have on my car. Will there be any damage in that short period of time, will my transmission fluid need changed or anything? or oil? or will it be alright now that I figured out what I was doing?

Thank you so much...