All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Your concern is valid because Allah the Almighty Says {What means}: "O ye who believe! Be careful of your duty to Allah, and be with the truthful." {At-Tawbah, 119}. This verse refers to every word, deed and with all people. Thus, it isn`t permissible to issue a receipt to the donor stating that he donated a greater amount than that he had actually paid.
Since you are in a non-Muslim country, such an act could distort the luminous image of Islam and make people, there, refrain from embracing it. Thus, don`t tolerate any deviation from the true path and may Allah protect you and bless you with success. And Allah The Almighty Knows Best.