I'm trying to say "I'm happy if you enjoyed..." or "I hope you enjoyed", but this is keigo, so I got a bit confused. If I were to say xxx 楽しんでいただけましたら、幸いです does that mean "I hope you enjoyed xxx" or is it not past tense, meaning "I hope you will enjoy xxx"?
This is not past tense. The ～たら is one of the conditional forms, regardless if it's a keigo or not. In this case, I wouldn't use this form because the condition is not necessary. Basically, it means you're happy if and only if they enjoyed.
I would say more something like 楽しんでいただいて良かったです。Literally "You enjoyed and I'm happy". This construction is very common.
One of the typical situation could be the following. (I'm not confident my English transration, but I hope you can understand the context and the nuance of "楽しんでいただけましたら幸い".)
Here is the ticket for Summer Grand Sumo Tournament. It's for you.
I don't know if you would be interested in it, but if I could have you enjoy it, I'll be happy.
This sentence "楽しんでいただけましたら" can be used for the future occurrence and the past occurrence.
The above example shows the future occurrence.
If you'd like to make clear the tense, you can say the followings.