Basement rough in question

I'm in the process of finishing my basement in my 7 year old house. The house has a roughed in bath but I am having problems figuring out the best layout to fit the existing roughed in plumbing. The attached picture shows a layout I created using cardboard cutouts for a 30" x 60" shower, 10" toilet and a vanity. The problem is the sink seams a little close to the toilet. I could reduce the size of vanity but I would rather not. Other then digging up the concrete, is there an easier way to offset the toilet closer to the shower? I have plenty of room to the back of the shower so I can easily push the shower back when creating the shower base. Another question I have is where do I drain the sink to? There is a stack coming down from the main floor bath behind the the vanity and another stack (maybe a vent) coming down behind the toilet. Will either one work?

Thanks,

The normal layout would be shower on the left, toilet in the center, and lav on the right near the door.
The santee is facing the wrong way for that, but it could be cut and swiveled around.

The 2" pipe on the right is probably the vent for the toilet.

I think you're right about the vanity being too close to the toilet. Minimum space is 15" on each side.

Is that from the flange O.C. ?

Yes, you should have at least 15" OC from the toilet. There's a minimum in front of it to a wall, too...think that is 24", but not sure. The rough-in is from the center of the drain to the FINISHED wall. Hopefully, it's more than 10" since at 10" your choices in toilets is limited (12" lets you use nearly any toilet).