I think you have some misconceptions about the rules
Here are some quotes from you in the comment section of your question:
I make them roll to see if they can land a hit or in the case of repairing armor to see how well they can use mend. I don't know the rules and even in the Players Handbook it doesn't specify exactly how cantrips work. I feel that the cantrip is not an 100% going to hit a target or do exactly what the player expects. That you still have to be able to hit the target.
The PHB is actually pretty clear on how spells (including cantrips) work. So much so that your will often find the phrases "There are no hidden rules." and "Spells only do what they say they do." all over this StackExchange.
Some spells do require a roll to see if they hit. Some spells require the target to roll to see if they can save off the effects. And some spells just work.
The Mending cantrip doesn't say anything about rolling for success. If you want to implement that rule, as a DM, that's your prerogative. But just make sure your players know before hand.
This other comment also concerns me;
So I was more making him roll to see how well he repaired his already broken armor that had been torn to shreds. His armor rating was a 23 and it was down to 2.
That seems a little impossible. The the Basic rules on armor class:
Without armor or a shield, your character’s AC equals 10 + his or her Dexterity modifier.
So getting an armor class of 23 isn't impossible with the right armor, shield, magic items etc. But how was the armor "torn to shreds" so that a peasant standing naked in a field would have a better AC? First, there are no rules for armor being torn to shreds. There are monsters and effect that can destroy armor, but just removing the armor would give the character an AC 10 (+/- 5) depending on their Dexterity. How did you arrive at an AC of 2?
I think you are adding rules to the game because you think they should be there.
Which is still completely valid. There are a lot of tweaks I make to the game when I DM. But all the players know about them ahead of time.
I would suggest going back and rereading the rules, especially the ones that you don't understand.
If they still don't make sense, ask the two players in your group that have experience. They should guide you in the right direction. Or check online forums as maybe other people have the same questions you do.