If you see a gap between the rail and the receiver top then either some of the mounting screws are loose or the rail itself is bent (less likely).  I would totally remove the rail, check it for flatness, clean the receiver & rail and, assuming it is indeed straight, re-attach the rail with a dab of removable thread locking compound on the screws.  I forget the torque specs (something like 15-20 in-lbs) but the specs are available elsewhere on this forum or Google it.
If the rail got bent somehow, I wouldn't try to straighten it but would replace it with the performance shop Elite Gen II hardened steel rail.  It would be a big challenge to bend that one!
Good luck
-Eric

I'm pretty new to this group and Tikkas but not new to shooting. I just got a tactical 308 last week and there was a screw in the threaded hole in the front of the rail on mine pushing it up about an 1/8th of and inch. I had the dealer remove because it didn't seem right. It is still slightly raised like what you are stating. While I don't believe it will affect accuracy I haven't been able to shoot the rifle yet. I read somewhere there is a reason for this hole but can't remember. I have to wonder, is there a chance it has been that way and you just noticed it?  Strange coincidence to my issue but thought I would post.

Sorry so long

if you can figure out how to take the pic rail off let us know, I cant for the life of me get mine off.

I believe the screw hole is for mounting a barrel strap / screen for stopping haze affecting your view through the optics.

I think the screw in there is just to fill the whole, but I think the screw is too long and when its screwed home it does cause the rail to raise at the front.  I have taken the screw out of mine and it hasn't affected performance.

I think this is a manufacture flaw that possible Tikka might not be aware of.

FYI.