If you think the sim is tough to land, just wait until you're on OE.... It's easy to let the plane drift to either side of the centerline.
If you're talking about staying centerline, i'd assume you're talking about a x-wind landing. The RJ can be tricky to land in x-wind, and there's soooo many ways to land this sucker in x-wind. Use the aileron to control centerline while you're on approach (crabbing), that gives you an idea how much rudder you need to kick when the time comes. Here's the kicker: Some people like to straighten the nose about 100', some 10', depends how "skilled" you are. This plane will not perform well in side-slip situation, FYI... I noticed the CRJ will drop the wing on the windward side when you kick the rudder, especially in windy condition, so be prepared for that as well. Well, all the above happens within 2 sec. before the mains touched down... I guess that's why you'll get paid some 20 bucks an hour...
I wouldn't worry much about the sim, as there's no good landing in the sim, and the only people you'll impress is the sim instructor, but on the line, the 18 year old bimbo sitting in the back will give you a pat on the back if you grease one
Good luck!