im a bad test taker

i study rigorously before a test and i feel confident i've studied when i take them. the problem is just that i think i have anxiety and my whole brain just blacks out when i take a test. i took an org chem exam last week and got a 74%. i studied hard for that exam and i just barely passed. it hurts harder knowing everyone else has higher scores than me.

what do i do in order to combat blacking out and being jittery?