The police had a warrant to search your room and got another warrant to search your car. A warrant means that a judge has heard a showing of evidence and believes that there was probable cause for the search.
Probable cause means a reasonable belief that a search would likely lead to evidence of criminal activity. A judge won't grant a warrant for police to go on a fishing expedition, because you have rights. There has to be a showing of enough evidence that the judge thinks they're going to find something, such as a tip from a confidential informant, as one example.
In any case, with these warrants, the police can search your house and your car. It's not necessary for them to get your permission. You don't have to be in your room when they show up, nor do you have to be in the car.
As far as Miranda warnings are concerned, you have conceded here that you were warned. They don't have to warn you again. You were informed of your rights and those rights don't change.
There may be things that the police did that were wrong and that can be challenged as you fight the case. But because they had warrants and because they did mirandize you, superficially, at least, the police appear to have been acting lawfully.