When they do the nerd makeovers, at the end, when the nerds are 'cool' they are now at different heights than when they were nerds. They are obviously different actors.
In the scene where Zoey and Chase are about to go over the rules, Chase sends the message and he closes the sidekick/tech mate. But when Zoey walks in the sidekick/tech mate is open and he closes it again.
When Chase accidentally sent Zoey the message about being in love with her, she should have received the message right away. But her TekMate never goes off and she never checks it.
When Zoey and Quinn find Dustin on the stair climber, and talk, Quinn's braid change from being in front of, to behind her shoulder a few times.
In the end when they are watching gender defenders and showing everyone playing they never show Nicole.
When they finally show the "Gender Defenders" beginning, they introduce each of the gang (Logan Reese, Quinn Pensky, etc). However, there was no Nicole Bristow.
When Zoey and Chase are about to go over the rules, Chase sends the message to Michael that telling Zoey he loves her may ruin their friendship. You can see that in the To and From section of the text message it says Michael instead of Zoey.