Problem With Trigger Is SQL Server Express

I am creating a doctor's office database for a class project and I need to create a trigger to prevent duplicate entries in the patient table. I am using the following code to successfully create the trigger. However, every insert on the patient table is rolled back, and the message prints, even if it is not a duplicate. Please help! Thank you.



CREATE TRIGGER trg_insert_patient
on patients
for insert
as
begin

declare @patient_name varchar(75)

select @patient_name = (select patient_name from inserted)

if exists (select 1 from patients where upper(patient_name) = upper(@patient_name))

begin

rollback transaction
print 'Patient already exists.'

end




end