It's been discussed over literally a thousand pages of the Forum.
Yes, he has been debunked. This tiny part of his recollection conflicts with the RADAR records of the flight, the FDR records, the damage path, and a majority of eyewitnesses -- including Mr. Lagasse himself, who saw the impact. The fine details are also inconsistent in several other respects (as pointed out even by other truthers). Furthermore, he does not support the conspiracy theories himself.
Bottom line, he is mistaken about the aircraft's precise location prior to impact. It happens. This is only interesting if you're desperate for an "anomaly" to bolster a preconceived opinion.
´This tiny part of his recollection´ has major implications wouldn´t you say?
His associate Brooks draws the exact same flightpath as him as pointed out in the video linked to.
The RADES data, FDR data and damage consistent with the proposed SOC flightpath are at odds with 99% of witness testimony who were in an actual position to see the final moments of the flightpath within the basin of land from the Navy Annex to the Pentagon facade.
The exception being Lloyd England

There are also serious questions raised as to the validity of the RADES/FDR Data here so I´d say this was far from contradictory evidence.
If Lagasse did in fact see an ´impact´ from where he was how can we question his testimony to seeing which side of the Citgo Gas Station he saw the plane on?
¨Obviously what I saw happened, therefore the conclusions made by people who didnt see it can be flawed...I accept the fact that there can be miscalculations on my part, but NOT whether or not the plane was on the North or South side of the gas station."
~Sgt William Lagasse after watching The PentaCon and responding to the ASCE
He is adamant in his testimony.
He is backed up by credible witnesses in the ANC area.
These 4 ANC witnesses in the video describe the approach as being over the right hand side of the Annex ´in a bank´.
Another ANC witness is George Aman who in his original CMH interview says
The plane flies right over the parking lot here
He also describes the bank mentioned by the other ANC witnesses.
Sean Boger supports Laggasse´s testimony from yet another angle. Actually on the Pentagon grounds at the heliport.
¨It would be on my right or the gas station´s left. If I´m looking out my window
Because I´m looking toward the gas station...it would be on my right hand side.¨
¨As he was coming towards me it just seemed like he was tilting the aircraft to
his right ¨
Or Levi Stephens?
He said repeatedly that it was on the "right" of the station or that it would be on his "left" if he was at the station facing the Pentagon.
He further confirmed by saying that it was on the "Arlington Cemetery" side of the gas station.
Robert Turcios?
They all put the plane NOC. They all had the best view. Most importantly they back up Lagasse´s testimony.
So before we jump ahead to any conclusions as to what his placement of the plane implicates,I believe the original poster´s question was ´has Lagasse´s testimony been debunked´
Opinions and possible explanations as to how he was mistaken linked to as a response are exactly that. Opinions.
He is supported by corraborrative testimony.
The accusation that he confused ´left´ with ´right´ is absurd and contradicted by no other witness. He saw it to his left.