I used 2024 Medicare deduction instead of 2023 and already filed 2023 taxes. Should I amend?

If your total itemized deductions were not greater than the Standard Deduction for your filing status then there is no need for you to amend your tax return.  Your medical expenses are itemized deductions.

Standard deductions for 2023

Single - $13,850 add $1,850 if age 65 or older
Married Filing Separately - $13,850 add $1,500 if age 65 or older
Married Filing Jointly - $27,700 add $1,500 for each spouse age 65 or older
Head of Household - $20,800 add $1,850 if age 65 or older

If you did take the itemized deduction and received a medical expense deduction, you would need to Amend Your Return.  If you did get a deduction for medical expenses and did itemize, you will find the numbers on Schedule A line 1.  

If there is nothing there, as DoninGA stated, there is no need to amend.