Using this calculator
http://realbeer.com/hops/bcalc_js.htmlI made a hop addition to match your numbers: 1.9 oz 10% AA added at 60 min.
For the original recipe (1063 OG 5.5G) the calculator predicts 50 IBU (you stated 49.9).
I then changed the OG to 1052 and batch size to 5G with the same hop addition. The new predicted bitterness is 61 IBU.
So, according to this Tinseth calculator your bitterness will have increase by 20%. 20% sounds like a lot but I think your beer should be fine.
Two things you can do if the beer is too bitter:
1. Water it down. Not recommended
2. Blend with another beer. Blending can yield great results.