Do you think my mother is being reasonable?

My little sister, only 4 weeks old had to go to the hospital in an other town 2 hours away. Me and my next door neighbour decided that I will stay over to her house and sleep up all night while my little sister, who is 7, slept over to my pops. See the thing is, I never wanted to stay over to my pops house, because it is boring there! So, after mom came back to get some stuff for my 4 week old sister, and told me to leave. I went to my neighbour’s house and was there for about 10 minutes, and I had my key so I went back in the house, and stayed there all night with my neighbour. The thing is, I told my mom that I slept there and went in the house in the morning. My mom found out I lied, and grounded me on Friday night! Me and my boyfriend was going up the bay, and no I am not aloud to go. Do you think it is fair that I am grounded, and not aloud out because I lied to my mom of one measly thing? I think its unbelievable! Is there anyway I could get ungrounded by tonight? HELP!