Under medical expenses, it says that I am below my threshold when my medical expenses total is over it. Balance due increases when add medical expenses is selected

You can claim the total of the eligible expenses minus whichever is less: $2,268 or 3% of your net income (line 236 of your tax return).

There are a few situations that impact the amount you can claim, you must be over 18, working and the expense was in the last 12 months. If you are claiming expenses for someone else they must be a qualified dependent. 

You can read more about medical expenses and how to claim them here: https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/tax-re...