First please confirm the right size and configuration of LEDs have been received, as the Free standing and Wall mounted versions are different lengths. If the sizing is correct, it's possible that the strips have been stretched.
To resolve this, start by installing both ends first, then compress the remaining part of the strip into the track. It’s also possible that applying a little dish soap will make it easier to slide the strips into the tracks.
If you have received the wrong LEDs, please contact customer service to organise an exchange.