"Oh, God, yes! I'm so glad we're here!"

I found a transcript of an online chat (remember those?) with Jen LePlante and Nick Schumann, two Columbine students, from the day after the massacre:
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Neither LePlante nor Schumann had anything terribly profound or earth-shattering to say, but it was still interesting to read their recounting of memories that were still very fresh.

Schumann was in the school store at the time of the massacre. He reported hearing someone say the following:
"Oh god yes, I'm so glad we're here."

This is the first I've heard of this - "Oh, God, yes! I'm so glad we're here!"

In the chat it sounds like Nick is saying he heard the statement himself.

Nick's 11k interview is on pg(4335 - 40) He was interviewed on May 6th 1999.
He arrived in the cafeteria at approximately 11:00a.m. Nick worked in the store in Rebel Corner and entered the stores office approximately 10 minuets later. After a student ran in informing them there was someone with a gun, Nick says he entered the cafeteria to look for his brother. Nick says he looked out of the window and saw a gunman, described as: wearing white T Shirt, white bandanna covering short blonde hair, dark pants and was of stocky build.
He and several others hid in the "Business" room. Nick says he lost track of time but heard what sounded like gunshots coming from the cafeteria. He said later he heard more gunshots and voices "whooping and hollering."
A note at the bottom on Nick's interview states that he had also been previously interviewed and that his previous interview had been videotaped. It's possible he could have mentioned hearing the statement in question in a different interview that is not included in the 11k.

Nick's girlfriend Tina who was located in a similar area was also interviewed pg(2454 - 2460). But does not report hearing the statement "Oh, God, yes! I'm so glad we're here!."  
She only mentions hearing two distinct voices saying "yeah, yeah, yeah" but doesn't remember anything else that was said.

From what I've read it doesn't seem like any of the other students who were hiding in the same area heard this statement either.

Nick's brother was also in the cafeteria when the shooting first started but left via the stairs, he does not mention he heard the above statement.

I could be wrong but i don't think any of the cafeteria witnesses reported hearing the statement  "Oh, God, yes! I'm so glad we're here!" when they were interviewed. This isn't to say it didn't happen of course, there are plenty of tidbits students mention when interviewed by the media or in chat logs that they do not mention in their official statements.