Certificate pinning - public/private key for license distribution - go

Question

I am trying to distribute an application - and need to add a software license to let the user use the application. I need some information to be distributed in the license regarding authorization(this works great using only public/private key)
Pseudo steps
Generate the public/private key
Embed the public key in the code
Create license using encoding
Distribute the license file
Application verifies the license using the embedded public key
6. Problem(using certificate to verify the origin of the public key)
Actual steps:
1 . Generate the public/private key
openssl genrsa -out private_key.pem 3072
openssl rsa -in "private_key.pem -pubout -out public_key.pem
2 - 5 And then embed the private key in code, and read a license file like(code from here):
func VerifyAndExtractPayload(publicKey *rsa.PublicKey, str string) (interface{}, error) {
var err error
str = strings.TrimSpace(str)
if !strings.HasPrefix(str, header) || !strings.HasSuffix(str, footer) {
return nil, errors.New("invalid license key")
}
b64 := strings.Replace(str[len(header):len(str)-len(footer)], "\n", "", -1)
var l license
b, err := base64.StdEncoding.DecodeString(b64)
licenseBuffer := bytes.Buffer{}
licenseBuffer.Write(b)
licenseDecoder := gob.NewDecoder(&licenseBuffer)
if err = licenseDecoder.Decode(&l); err != nil {
return nil, err
}
hashed := sha256.Sum256(l.Payload)
if err = rsa.VerifyPKCS1v15(publicKey, crypto.SHA256, hashed[:], l.Signature); err != nil {
return nil, err
}
var payload interface{}
payloadBuffer := bytes.Buffer{}
payloadBuffer.Write(l.Payload)
payloadDecoder := gob.NewDecoder(&payloadBuffer)
if err = payloadDecoder.Decode(&payload); err != nil {
return nil, err
}
return payload, nil
}
Then I realised that maybe I should use certificate pinning, so no one can replace the public key.
Pseudo code:
Generate a root certificate using private key
Embed certificate
Generate license like above
Read public key from the certificate
Application verifies the license using the embedded public key
Questions:
How to verify read the public key from the certificate?
And is the public key now verified?