Compare client certificates in go

My use case looks like I know the client's public certificate and just want to allow them. I have a go server configured based on gin and TLS where a method has been assigned to the property "VerifyPeerCertificate". The function looks like

func customVerifyPeerCertificate(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error {

if len(verifiedChains) < 1 {
    return errors.New("Verified certificate chains is empty.")
}
if len(verifiedChains[0]) < 1 {
    return errors.New("No certificates in certificate chains.")
}
if len(verifiedChains[0][0].Subject.CommonName) < 1 {
    return errors.New("Common name can not be empty.")
}

fmt.Println(verifiedChains[0][0].Raw)

publicKeyDer, _ := x509.MarshalPKIXPublicKey(verifiedChains[0][0].PublicKey)

publicKeyBlock := pem.Block{
    Type:  "CERTIFICATE",
    Bytes: publicKeyDer,
}
publicKeyPem := string(pem.EncodeToMemory(&publicKeyBlock))
}

But the problem is that the string in the variable "publicKeyPem" doesn't look like the client public certificate I use to send requests to the server, it's also shorter in length.