I would call that to be on the light(ish) side of Medium...So..Medium Thin?
I usually figure a Med starts at around 4-1/2 Lbs...(2040g) for a 20"...
so,you are around 2 ounces light of that....
It should flex pretty good if you flip it over (looking at the underside of the bell) and grab at 3 and 6 o' clock,and try bending it with both hands...
Hope this helps....