I am trying to change the auto trans fluid on my 2002 isuzu rodeo 3.2L rwd automatic transmission. I found out about the drain and fill plug online and followed the steps that I read.

The problem is, first I loosened the fill plug to check the fluid and it started pouring out, as if it was the drain plug, I was under the impression that it should just dribble out if the it was at the right level. I ignored that and proceeded to the drain plug and drained the rest of the fluid, after I finished this, I tightened the drain plug(the recessed bolt in the center of the pan) and I stuck a tube in the fill plug and started pumping new fluid in. As soon as I finished, I pulled the tube out and out came all the new fluid, pouring all over the ground.

Why is the fluid pouring out of the fill plug(the higher plug in the back corner of the passenger side of the pan)?

All of this was done while the car was off, is this my problem? I am not familiar with automatic transmissions, but I thought I could undertake a simple task as changing the fluid.

Please help me asap as I am going on an 11 hour trip as soon as I finish this. Thank you.