If you're going to fudge things because your players are new and haven't learned all your tactics and ideosycracies yet as a DM... then the place where I think you should fudge is the hill giant and "3 ogres" outside the mine.
Your rules for long rests and leveling up through long rests should not be fudged, because you intend to use those rules throughout your campaign. So if you change those rules now, they mean much less in subsequent games as the group will think you will always be willing to give in and fudge if they get themselves into trouble when needing a rest in the future.
But your formatting that you had three ogres show up to supplement the hill giant outside the mine? That's merely a story point, not a rule. That is one where you can easily change or evolve the story to be nice to your group, without it impacting future adventures.
Yes, you had the three ogres arrive so that the group wouldn't just leave the mine willy-nilly. Well, they haven't done that. At this point they are leaving the mine because they HAVE to leave the mine if they wish to get to any place of safety. So letting them do so in some form or fashion is the best way to go. Did the group see the ogres arrive to help the hill giant before they entered the mine, or is this just something that you said happened in the background while they were inside? If the party doesn't know the ogres are there, then you can make up any excuse as to why one or more of them aren't out front any longer. Maybe they got bored and left the hill giant, or maybe other creatures arrived in the area and the ogres ran off to deal with them and aren't out front anymore.
Say whatever you want, so that if the party does try to go back to camp for a long rest, maybe they only face the hill giant and one ogre, or perhaps just the hill giant itself. Just make up any excuse for not having the additional ogres there to kick the crap out of the party if they try to leave. If you do this, you still aren't making it easy for them to retreat out of the mine because they still have the hill giant, but you also aren't kicking them when they are down for no reason (which you would be doing if you threw the hill giant and three ogres at them.)
The group should realize that resting in the mine is suicide. So let them try to leave, and only face down the one hill giant they didn't take out as they entered so they learn that lesson that enemies you leave behind will still need to be dealt with later. That's my suggestion.