When my car was parked up, somebody hit the front right-hand side and left a scratch.
The front right-hand side of my car was hit when the car was parked up.
My car was parked up legally, but somebody hit my car and damaged the front right-hand side.
右前方
Right-hand side = On the right
車の前方は、noseという単語を用いる場合もあります。
The front end of a car can sometimes be referred to as the "nose".
また、日本語同様bonnetという単語も使用できます。
The cover which goes over the engine is known as a "bonnet" in British English, and a "hood" in American English.
You can specify that the car was parked up in a legal parking spot (i.e, a parking lot) but it is not necessary if that information was already spoken about. I would assume that the main information of this point is that the car was hit when it wasn't being driven, and also where on the car body it was hit.
While my car was parked, it got scratched on the front right-hand side.
The front right-hand side of my car got scratched while it was parked.
While my car was parked, someone scratched it on the front right-hand side.
英語で「車を停めていたら、前方右を誰かに擦られてしまった」は「While my car was parked, it got scratched on the front right-hand side.」又は「While my car was parked, someone scratched it on the front right-hand side.」と訳せます。「Got scratched」の例の方は受身形ですが、「got」は、「～られてしまった」のニャンスを強調します。
車を停める = park the car
誰か = someone
前方右 = front right-hand side
擦られた = was scratched
例：
車を駐車場に停めていたら、車の右前方を誰かにぶつけられてしまい、擦った傷が残ってしまった。
While my car was parked in the carpark, someone bumped into the front right-hand side of it, leaving a scratch.
お役に立てたら幸いです。
イギリス 
オーストラリア 
