For me it was just a "bigger" version of middle school. You have a wider range of ages and a lot more students so it was intimidating being 14 and around a lot of 17-18 year olds. 

You have to remember, all the worry you are feeling is not exclusive to you, there are so many other kids that are going into high school nervous and afraid or without friends.  

Just do your best and focus on school, the friends will come naturally. Don't hesitate to walk up to other kids at lunch who are by themselves and make a group out of it. There's a good chance you will meet some of the best friends you ever had when you start.