Your test kit is fine. Just wanted to you be aware of the effects of ammnolock on some types of kits.
Continue water changes till nitrite is 0 along with ammonia and nitrate should be less than 50ppm.
I am very concerned its that high after just a short time period. I was thinking it was from overfeeding but if you feed only every other day unless you feed ALOT every other day then I am at a loss as to why its as high as it is.
I would remove the UGF
and also have the CC substrate of 1/2" - 1"
Personally I like a DSB
(Deep Sand Bed) for my substrate.
Dont worry your LFS
did not steer you wrong they just sent you down a bumpy road.