Usually, on a rail (base) there will be 2 screws in the front and 2 screws in the back. IDEALLY, if you tighten only the front or rear pair with no screws in the other 2 holes, there should be (almost) no gap between the top of the receiver and the bottom of the rail. If there IS any appreciable gap then you should probably consider bedding the rail. The gap pictured is grand canyon scale in my limited experience.
What I would do is remove the rail completely and closely inspect and clean up the rail, the screws, and the receiver and then trial fit the rail with just the front pair of screws snugged (NO rear screws) and look at the back of the rail for a gap. Then reverse the process with only the rear screws used/snugged (NO front screws) and look at the front of the rail for a gap. If you can't see a gap, tap (firmly) on the end that could have gapped and listen for a "click" of metal contact. If you can's see a gap but hear a click, there is a small gap - look closer with a light/bright background...
As I said, if you have any appreciable gap (> or = 0.010") on either end, you should consider bedding the rail. If you have never done rail bedding, there is no shortage of YouTube videos on the subject... watch a few and then try it, it isn't difficult.
Also note: When you are snugging either the front pair or the rear pair of screws, BOTH screws should snug down individually securely holding the rail. On the off chance that one of the screws is TOO LONG, it won't tighten down correctly. This also needs to be fixed by either getting a shorter screw or shortening the screw you have. This "long screw" problem happened to me when I was mounting a rail on my R700.