Solid Hardwood, Engineered and Laminate Flooring - Sanding Stop and Start Marks on the Floor / Please help

To start, we sanded the floors with the proper grits of sand paper 20, 60 and 80 (or 100) can't remember. We have put the minwax dark walnut stain on the floor and now you can see where the drum sander started and stopped about 2/3rds down the room (there's a line). Some parts of the floor are darker and some lighter. Could it be we didn't sand enough with the 80 grit paper (we used this paper with the drum alot more quicker than the rest of the grits)?

I have 2 questions....#1 can this be fixed by going back to just add more stain to the lighter areas and #2 you can't see the differences much when the stain is initially put on and still wet. Will it look the same when the MINWAX poly is put on to finish the job?

This is our first job, and we know it won't end up looking professional but we just want to try to do it the best we can without re-sanding again.

Thanks in advance for your help, please hurry in your responses, we are finishing with poly tomorrow night.

Stain shows every imperfection in the sanding job...........after you apply the stain, but you already know that. After sanding with the big machine, you need to use a floor machine(buffer), increasing the grit to fine. That usually gets out all the big machine marks. At this point, the only way out is to start over, otherwise it will be blotchy. You may be able to go over the floor with the buffer and start with a course grit, but I suspect you need to start at a finer grit with the big machine. I hope you have not done the poly yet, that just compounds the problems.

Also darker stains tend to highlight sanding problems where light or no stain isn't as critical.