Taking my parent's car for a small drive. Am I in trouble?

Just about 2 hours ago, my parents left, and said they would be back at 11pm. Right now, it is 8:40pm, and there's a spare car in the garage, that only is used when 1 of my parent's 2 cars breaks down.

I'm 14 years old, about 5'6'' and I took out the spare car, and 97' Honda Odyssey, for some driving on a private road. I did not go on the double yellow line roads, I'm really afraid that I will be in an accident. I have driven it around for maybe 40 minutes, and parked it back in the garage. The thing is, I feel extremely horrible about this, and I'm freaking out that when they come home, they'll see something that is off, and know I took out the spare car. I never went above 25 mph, and I'm really afraid. I never defy my parents, and listen to them always. They aren't that strict, but I think if they find out, I will be punished severely. Should I just wait, and will the guilt just go away? Should I just confess? Please help me.

Added (1). No, I didn't get into an accident.

How much extra if i pay in full?

I have saved up $20,000 to buy a Honda odyssey I want to know if I got a car for the exactly 20 grand how much would the Tags, Title and Taxes be in Maryland? No I don't want financing Yes paying full price up font.

My engine makes a weird noise sometimes when I drive?

I have 2008 Honda Odyssey DX. When I'm driving, there's no problem up until I drive up a slight hill. There's a cranking/grinding sound ONLY when I press the gas and I'm driving up a small hill. It stays for about 5 seconds and then it goes away. Any idea to what it could be?