Yours looks to be 3 gallon, as well as correct for the year.
Photos below are of four gallon from 1950, note recesses at knee areas that had screwed in grips or plates the grips would mount to. A center seam was run about 1952 on, giving a slightly different shape, but still with indents. Wider tank lines on the four gallon, oh heck, let's face it, that dang 4 gallon tank is just fat!
(Ummmmm, by the way, have you tried to see how many gallons of gas can you pour into your tank?)