Re: could this be cancer in my big toe??????
As Oleander stated, what you have may not be skin cancer. Fungis is actually quite typical and looks very similar to what skin cancers look like. It could also be a bruise and is slowly growing out - I had a bruise on my big toe that took a full year to grow completely out, and for the longest time it didn't look as if it was moving.
So, you say your appointment is on Friday? That's just a couple of days away. You are doing the right thing by having this checked out. Try to relax and work with the doctor. Actually, while skin cancer can develop under toe nails, it is not all that common. Try not to worry unless there is something to worry about - at least, that's what I try to do!
Oh, and keep us updated!