True repentance involves repairing damages done (where possible). In this case, it would mean returning the money.
Leviticus 6:2-7 (KJV)
2 If a soul sin, and commit a trespass against the LORD, and lie unto his neighbour in that which was delivered him to keep, or in fellowship, or in a thing taken away by violence, or hath deceived his neighbour;
3 Or have found that which was lost, and lieth concerning it, and sweareth falsely; in any of all these that a man doeth, sinning therein:
4 Then it shall be, because he hath sinned, and is guilty, that he shall restore that which he took violently away, or the thing which he hath deceitfully gotten, or that which was delivered him to keep, or the lost thing which he found,
5 Or all that about which he hath sworn falsely; he shall even restore it in the principal, and shall add the fifth part more thereto, and give it unto him to whom it appertaineth, in the day of his trespass offering.
6 And he shall bring his trespass offering unto the LORD, a ram without blemish out of the flock, with thy estimation, for a trespass offering, unto the priest:
7 And the priest shall make an atonement for him before the LORD: and it shall be forgiven him for any thing of all that he hath done in trespassing therein.
If you don't return the money then you haven't truly repented.
Notice Numbers 5:7 even suggests you should return more than you take.
Then they shall confess their sin which they have done: and he shall recompense his trespass with the principal thereof, and add unto it the fifth part thereof, and give it unto him against whom he hath trespassed.
See also Ezekiel 33:15, Luke 19:8.