I began an new start early last week, only to find MOLD in my start on day 4!!! Not sure I'm cut out for sour dough...
I had the same - I wouldn't worry about it.
Toss the moldy starter and begin again. Look at it as chalking up experience. :) Practice makes perfect as they say.
When this recently happened to me on day 2 or 3 I decided that I would go for safety in numbers... I made several starters.
In fact I just finished my day 7 feeding all four of them in just under an hour. LOL! It's like having... err... kids.
Keep at it.
If you use pineapple or orange juice instead of water for the first four days you won't have mold. The acid in the juice prevents the mold from growing. Trust me, it works!