Everyone use "were" / "was" it's interchangeable.
But you need to remember, that everyone can be followed by two of them.
--> You may use "were" when you are facing subjunctive/conditional form, for example :
"if everyone were happy, I would appreciate on them"
Otherwise, when stating factual statements, it should be "everyone is (or was) present", example --> everyone is great today / everyone was great.
everyone except me was, --> because it's factual statements, however it can be replaced by "were" if it was conditional sentence.