Why is my ARM APR so high?

In MC, the APR on an ARM is determined in part by which scenario you choose for the adjustments.

Best Case:
In a Best Case Scenario the Interest Rate will move to (Index + Margin) at the First Adjustment. It will then stay at that rate for the entire life of the loan. This option typically presents a low APR (often lower than the note rate) because the maximum amount of payments on the loan will be at the lowest rate. This is the one you should use if you need to match the APR to your LOS. For compliance though, make sure to note the max payment somewhere in the more info sections in the presentation screens.

Worst Case:
In a Worst Case Scenario the Interest Rate will increase by the amount of the First Adjustment Cap at the First Adjustment. It will then increase by the amount of the Periodic Cap at each of the future adjustment points until it hits the Life Cap. This option typically presents a high APR because the maximum amount of payments on the loan will be at the highest rate.

Custom:
In a Custom Scenario you define the Adjustment Points and the amount of each adjustment. The APR presented will be based on the total monthly payments for the entire amortization.

What MC Support usually recommends is to show both a worst case and a custom option so the borrower can see both angles. For your custom option, you can specify much smaller adjustment and even space them out over more time to look more like what the index values have historically done.