Again, it was twice.
Testimony from Nelson Degado
Delgado. Delgado claimed many things, but his claims contradict the established record. In his recorded testimony, Delgado can't keep the ranking of ratings in the Marine Corps straight in his head. For example, you say that 210 is the cutoff point for marksman, while Delgado claims in testimony that 170 is the cutoff point for sharpshooter - one ranking above marksman.
All Delgado is certain of is that he himself was an excellent, excellent marksman.
When Oswald lived in Minsk he belonged to a gun club there and members also reportedly said he was a poor shot.
How many gun clubs were there in Soviet Minsk?
Carlos Hathcock, who shouldn't need any introduction, examined the shots and tried to duplicate them at Quantico
I have yet to see the document in which Hathcock himself directly makes this claim.
Many things are said about Carlos Hathcock, but few are documented outside of official Marine Corps records.
Regarding Delgado's testimoney concering Oswalds shooting, it matches that of Oswalds military record in that he simply wasn't a talented shot.
"Let me tell you what we did at Quantico. We reconstructed the whole thing: the angle, the range, the moving target, the time limit, the obstacles, everything. I don't know how many times we tried it, but we couldn't duplicate what the Warren Commission said Oswald did". (KILL ZONE, pp. 89-90)