You should not be worried.
For any given subject there is a finite number of sources which can be referenced. So it's highly likely that you're referencing the same sources which multiple people have referenced in the past. This is why your lecturer has told you this is quite normal.
Was is odd, however, is that your reference section consumes about 43% of your whole paper. Is that right? So a 10-page paper contains about 5.7 pages of content and 4.3 pages of references?