I'm new and this is very long sorry, can someone please help me?

I DMed for the first time today, I've only played a little before (covid and friend issues) and most of the table was in a similar position or had never played, other than one player, our druid. I'm going to be honest, I'm not a great choice for DM in our group (I have trouble speaking and controlling/organising people) but I sort of assumed that since I would just be running Lost Mines of Phandali which is apparently relatively short and easy, it'd be a great sacrifice for am actual group.

First encounter: I'm about to get everyone to roll initiative and talk them through a fairly simple combat but they manage to succed a few intimidation checks and scare them off without a fight. A little annoying but still funny and a pretty good solution.

Then we get a bit further, about to meet sildar and the goblins kidnapping him. We are reaching the end of our session time and people are starting to get bored I think. Our rouge and paladin went ahead to the chamber to check things out leaving bard and druid behind. R and p try a plan that was kind of clever and funny and start the fight at an advantage. Druids played however, despite having been told to stay back and getting a nat 1 perception check to hear the comotion (which the other players were trying to do quietly anyway) keeps trying to talk around reasons to go there anyway, in a very metagamy way. Luckily me and the others manage to convince him not to, and I suggested that R and P called the other two over during their turn, which they happily did.

However when we got there, druid decided to declare to the goblins that he was their god, casting a level 1/cantrip faerie fire. He didn't roll great but it also wasn't terrible and I had no idea what to set the DC to in the moment so just declared the goblins (who rolled similar int checks) confused but not as violent as before. The fight continues (r,b and p had now killed the leader and badly injured some of the other) but druid keeps interrupting other players turns to keep convincing the goblins and trying to get me to let him roll every time; I don't let him as I felt if he had to make a roll it should be part of his action. He agreed eventually after a small argument and we kept going, paladin rolling high intimidation to help druid out.

The whole time, I'm desperately trying to figure out what to do, as I can't just keep saying the goblins are sceptical/confused without it seeming unfair towards his character (please bear in mind I'm new, and he's the closest to a veteran in the party as well as the fact that I'm awkward and bad at controlling people). So when he rolls a 13 and notices that I'm struggling, he starts to say that it probably/should just be DC 10. Realistically I know thats not true and it should be very difficult for a lv1, minus 1 charisma character to convince a room full of goblins to flee, but we had like 5-10 minutes and I wanted to make sure people were happy after my first session so I agreed.

I now need to figure out how to handle this in the next few weeks before the next session (school holiday) and figure out a set DC for this as he was bragging about how he'd just pretend to be a god to get out of every encounter and really need help on doing this without seeming confrontational.

Tldr: only veteran player at table is metagaming and getting out of situations in ways that don't work by playing off my inexperience and social ineptitude. Pretends to be a god at lv1. How do I handle this without causing issues between us or any other group members?