Hi I've been riding for 4 weeks now but was riding at a younger age now I'm scared to canter but I love horses too much to give it up. In the past 4 weeks I'v fallen of a cob and been on a runaway pony so am pretty scared to canter got any advise for me?

Relax! When I first started cantering I felt the same way you did. Long story short I had seen my mom fall off, so naturally I was afraid to start cantering. My trainer was persistent and we eventually started on the lunge line. It was actually really fun! I learned that cantering is just another gait. Now I'm working on getting over my nerves about jumping 3'!
Anyway, are you working with a trainer? If so, you should talk to him/her about your fears. They can help you get over them by taking it slow. Maybe you need to build up your confidence more at the walk and trot on different horses. It's okay to take your time. You don't need to rush into anything.
Being on a runaway is pretty scary! Just remember your one-rein stop. However, in some situations if your horse is really frightened you need to just let him run a few strides then circle him at the canter or trot. Just like falling off, you need to chalk it up to experience. Now next time you will already know what a bolting horse feels like, so you will be able to act accordingly or try to keep their attention on you more.
As you already know horses are animals and are unpredictable. You are probably going to be on more horses that shy and buck and bolt. You just need to be prepared and stay calm. You could fall off your horse at a walk. Like I said, cantering is just another gait and you will have so much fun once you give it a chance!
Best of Luck! Tell me how it goes!

For a canter, be sure to change how you sit on the horse. For instance, when your horse trots, your teeth will rattle if you don't sit a certain way and move your body a certain way. A canter is much more fun and easygoing. Once he goes into that gait, all you have to do is slightly change how you sit and move and it will be like you are riding on a big rocking chair.

Let your instructor or another rider demonstrate the two different seats and the way the rider moves for each.

Simple answer is "don't canter". I'm not being facetious. Sometimes you just need to take a step backward to move forward. Work at the walk and trot. Set up patterns and have a good time. Play games. You'll be surprised when one day your horse just moves into the canter and you barely notice the change. It sounds as if you are being rushed into advancing too quickly because your instructor (please say someone is teaching you!) knows you rode before or because you got overconfident about having ridden in the past. And if you're riding ponies that belong to friends but are NOT school horses, you need to stop doing that. I love my horse friends, but some of the horses they love are just scary and unpleasant and I wouldn't get on them on a bet. My own horses are bad enough sometimes.

And work in a confined space. A "runaway" suggests you were out in the open in an unfenced area. For someone who's been riding for four weeks, that's not safe and it's likely to wind you up in the ER. Start by learning to control yourself and the horse, then you can work on riding faster and doing more.

I would stick to trot for now, just to get your confidence back. Make sure you feel completely comfortable and in control until you move up into canter. Practice lots of sitting trot keeping your upper body in the correct position, keep you legs long and relaxed. As soon as you tense up and grip on with your legs you'll find your much more perched on the saddle instead of sitting deep and keeping your heels down. Master this, and then move on to canter when you're ready and on a sensible horse.

I understand, I am afraid to canter too, when I was young i used to be able to canter but now as an almost 50yo woman I am scared. I have taken lunge lessons on several horses and cantered a few strides on one . My seat is a bit more secure now, but that fear is still there. Yes, I am afraid of falling. I have only fallen 2 times and that was in my forties..