Well its not something to be worried about. When you book a car in your name, and pay the tax along with invoice, the FBR gets to know that you bought something. What they do is they write a letter to you and in the meanwhile send querry to state bank to know about accounts opened by your ID card.
Now what you need to do is register at FBR (completely free, can be done sitting at home), then apply for FBR certificate online . In this process you have to mention all your accounts plus your primary account ( if you are salaried individual).
Within a week, you can goto your respective FBR office nad collect your certificate (no charges at all). Now you have to apply for online TAX return and wealth statement disclosure on that same FBR site. you'll receive your login information via three different sources (email + sms + letter). Once you get all that, go online and file your tax return.
Now the core solution to your problem lies with wealth statement which goes with tax return. In that statement, you HAVE TO mention that you had a gift money from your father/mother (even if you sold a car that was in their name) and with that money you bought that asset (New car). Its a 2-3 weeks procedure (sitting at home). Thats why they give you about a month to explain yourself about that purchase.
Hope it all helps