Please read in this page the following about the free $200 dollars trial:
We’ll never charge you unless you decide to move to pay-as-you-go pricing. If you move to pay as you go, you’ll only be charged for services that you use above the free monthly amounts.
Once your consumption reaches 200 or the time limit you will have to move your subscription to pay-as-you-go to continue using Azure resources. But you won't be charge while the subscription is set as trial.