Refused cuz I didn't offer the custodian declaration, applying again with it now

[Wendyren]

I was refused for my application for the study permit extension because I did not offer the custodian declaration and I am under 18. Now I start to apply again for the study permit and I offer the declaration in the letter of explanation. Will I get my study permit this time (Because according to the refusal letter the officer did not mention any other thing incorrect) or will I be refused again?

I am so nervous right now and I need help.

Also, how can I include the receipt to my application if I both submit and pay the fee online?

Thank you in advance for your time.