This was entirely appropriate. You have nothing to complain about.
Do you think spellcasters should spend their own hard earned gold to help you out? Spellcasters are generally the only ones that significantly need gold in AL play. Having people set aside gold if they think they'll need Revivify is a good suggestion on the cleric's part. I'm sure others could pitch in to Revivify a poor character if they want, but why should it all be on the back of the cleric? And should you also force your party to lose money because you can't/won't budget for it? If I were the cleric I'd just let you go into TCP debt to get an NPC Raise Dead afterwards if you were going to try to force me to pay for your Revivify. (Treasure Checkpoints and debt for raises is explained in the AL rules.)
If he had just taken the money and kept it that would be one thing, but since he returned it at the end of the session, it was basically just ensuring you had the necessary material component on hand and weren't going to be a mooch. (I'm not sure why you needed to give him 2 up front, though, you could have just given him one and then given him another if you got Revivified the first time - you'd still need to have the dough and have procured 2 300gp diamonds, however.)
You could argue "well, just take it off my body if it's needed to heal me." That'd work fine for an after-combat Revivify. But depending on how strict your particular DM is about things, it'd complicate an in-combat rez, so having it already in the cleric's hands is most prudent. And if you're going to get it back guaranteed because of AL rules, I'm not sure what the problem is.
You should get really used to it, because now in Season 8 they changed the gold rules to where people don't really get gold except fixed amounts at level-ups, so everyone is more gold poor, and spellcasters are the only ones that need much of it, so things like Revivify will be even tighter and everyone less able to chip in in the future.