Carrying a knife or any weapon isn’t a good idea. Carrying a knife or a weapon for someone else is an even worse idea. 
Some people believe that everyone carries a knife or that carrying a knife will some how offer them some protection. But this is not the case. Believe it or not, not many people actually carry weapons or knives, it is actually illegal. Very illegal, and if you are found with a knife on your person, you can expect to be in a lot of trouble. Big trouble. 
Carrying a knife does not offer protection what so ever. If anything, it encourages violence, it increases the risk of being attacked, you are more likely to be attacked if you are carrying a knife. 
There is no reason to be carrying a knife, studies have shown that being assaulted by a stranger is extremely slim, you are more likely to be assaulted by someone you know, and this is not a worry you should be experiencing. You need new friends if this is how you feel around the friends you have now. 
Research has shown that individuals who carry a knife are more likely to be assaulted, this is because carrying a knife makes you a threat to others, to people you may know. Carrying a knife does not make the people around you respect you, all you are doing is encouraging fear and fear encourages conflict. You are more likely to be attacked due to carrying a weapon in order to prevent you from attacking others. If you are a threat, the people around you will try and reduce that threat by attacking first. All you are potentially doing is putting a big target on your back. It does not sound like a fun environment to be in.
The best way to be safe and to reduce any risk you may be feeling is by leaving the knife at home, or better yet, go to your local police station and hand it in. You won't find yourself in trouble by handing it in, if anything you will be respected so much more, not only by your friends but also by the police. It is better to be on the side of the law rather than against it, believe me, the last place you want to find yourself is in the dock of your local crown court being sentenced to prison. Carrying a knife for yourself or for someone else will result in a severe sentence, expect to recieve a hefty fine too.  
It doesnt matter if you carried the knife or not, or even if you did not carry out the assault, you will still be in trouble, you are still just as responsible and accountable in the eyes of the law and you will be punished and sentenced just as harshly and as severe.
Prison is not a badge of honour, or a place you want to go. Prison is dangerous and for someone who is young? It can be destructive and possibly the worst experience of your life. 

It is not just knives and weapons, you may be asked to carry other things such as drugs. Carrying drugs for others can have very severe consequences. It doe not matter whether you are using them or not, it is the danger that the drug poses to society that is taken into account. Drugs can destroy lives, and can lead to the loss of life, if you are carrying drugs for yourself or for someone else, the law will see this as an intent to supply, even if you are not dealing drugs, it is the opinion that you will share these with your friends, this is defined as 'intent to supply'.