Certificate pinning - public/private key for license distribution

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

1. Generate the public/private key
2. Embed the public key in the code
3. Create license using encoding
4. Distribute the license file
5. 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:

1. Generate a root certificate using private key
2. Embed certificate
3. Generate license like above
4. Read public key from the certificate
5. Application verifies the license using the embedded public key

Questions:

1. How to verify read the public key from the certificate?
2. And is the public key now verified?