Couple of Problems

I've began growing for the first time and all seems well so far but when I went and checked on my plant today I had a couple of mushrooms that popped up over night. I assume this means that I am over watering my plant, but I just want to double check and make sure. What should I do?

Also when I planted my plant my friend kept suggesting that I plant two in one pot, so I did. Then when one of the seeds popped out of the soil I just removed the other. Now I am growing a plant that is far to the left instead of in the center. Is this going to effect my grow at all?

I am growing in a small pot just to begin with, and it is an outside grow

It will be ok in the side of the pot for now. It can be fixed you you repot or plant in outside.
make sure to water when its dry. stick finger in the dirt to get a feel to see if its dry.
Most watering problems comes from watering when the plant does not need it. Not the amount of water just to frequently between dry times.

Yes let it dry our between waterings. I stick my finger in the bottom hole to see how dry. And as mentioned you can fix the plant position when you re-pot it.