Why do the police need to know what I was doing?

To cut a long story short, i told my parents i was out job seeking in the city centre when I actually was with my boyfriend at a park where i got robbed for my iphone and threatened with a knife at 2.30pm after he left me alone for 5 mins. I made a statement with the police, being 16 i needed a parent there. Since my parents was there i had to lie about the whole thing. I said that i went to the city centre and at 2.15 caught the bus to the park to meet with a friend and together we came home (we live close) and it was at 2.30 i was robbed. So i lied about arriving to the park an hour after I actually did since my parents don't let me out to socialise with friends, i'm not allowed a boyfriend. Will the police inform my parents i got off the bus at 1 (bus cctv) and if there are any footage from the park, will they show i'm with my boyfriend? :/ i have an incredibly strict family, i will never be allowed out again if they know. I live in England if that effects anything.

I don't believe you… You lied to your parents and you lied to the police

You would have signed your statement to say it is the truth, by lying you have committed an offense and can be prosecuted, so your parents will find out when you're arrested.
Also if the offender was found (and they might as iPhones can be tracked quite easily) and the matter went to court the defense would only have to cast some doubt on any part of your statement to have the whole case thrown out.