I wouldn't use the ruse of a "loan" to your parents because that is simply untrue, lying about it and being caught in a lie could be a problem. Especially as they never used the money, there is no evidence that it is a true loan. They were holding it on your behalf, they were not recipients of a gift or a loan so they didn't benefit from it unless you could count any interest that they earned on it (I am assuming that from yours and your parent's perspective any interest would rightfully be yours unless you agreed it with your parents as a form of payment for them holding your money for you).
If it is queried and you have documentary evidence demonstrating the origin of the funds then your explanation is perfectly reasonable and rational. The money never left you, your parents are just returning what is rightfully yours.