I remember my university entrance ceremony as if it were yesterday.
I remember my university entrance ceremony like it was yesterday.
as if it were yesterday が正しいです。
as if it had been yesterday は違う意味を伝います。If + had been を使いますから条件法の文章になります。「入学式があったらとして、まるで昨日のように覚えている」という意味になります。
よりインフォーマルな言い方も可能です：
I remember my university entrance ceremony like it was yesterday.
オランダ 
