For starters, w/o knowing exactly what you're doing, there's a difference in REDOING and REFINISHING a hardwood floor. I'm going to assume (for the benefit of others that might read this post) that you're REFINISHING your floor (since you're asking about staining.)
In any event, you may want to review these 2 links about refinishing a hardwood floor.
Again, be sure you're reading about what needs to be done in reFINISHING vs. reDOING a floor. I'm recommending you kinda 'take a break' to see if you missed anything. I will say that Maple by 'nature' is a tightly-grained wood and will show scratches and marks a whole lot more than many other floors. You may need to go a little higher in the sandpaper grit. For testing your 'efforts' with sandpaper and stain, either pick inconspicious places on your floor, like the closet or part of the floor that's going to be covered w/furniture or something, to test your work out. OR, buy some maple from the store, finish it up by 'hand', and review the results.
I'm betting that you need to go a little higher with the grit. My best to ya and hope this helps.