It's pretty unusual to get the elastication absolutely right first time. Often you will err on the side of caution and things will be too loose, with the connector hanging out of the end.
Before you cut an inch or so off though, be sure you've lubricated the inside of the pole with one of the many pole lubricants available, because it could only be friction or a piece of dirt which is stopping the elastic sliding back in. If it's still hanging out, you may need to tie the connector on again, only a little further towards the bung.
Ideally the connector should slowly slide back to the PTFE bush.
If it snaps back you have done it too tight.
In either case, the bung I use comes in really handy. I use a Vespe bung you can wind elastic onto, which I do before I tie the connector on. This way, if things are too tight I can simply unwind a coil or two off the bung's winder until things are spot on, or wind a turn on if it’s too loose.
One strange phenomenon you might comes across is that you have set your elastic perfectly up at home, but as soon as you start using it and catching fish, it starts hanging out of the end. This is bad news as your line is very likely to tangle around the elastic and connector, and high tech line and pole elastic make for impossible tangles.
This usually happens because you haven't fully stretched the elastic before putting the connector on.
The best solution in this instance is to give the elastic a good old stretch until it 'bottoms out’ (won't stretch any more), and then tie the connector on again, taking off a little elastic at a time until it gently slides back to the bush.
Another possibility is to use what's called a 'tensioner', which you can buy in most tackle shops.
This neat little plastic device sits inside the pole just above the bung and all you do is wrap the elastic around until it’s ‘just right’.
Tensioners also help during a session when you could do with stepping up in elastic size (say you start catching bigger than expected fish, or need to catch more quickly in a match situation) but don't have a spare top kit set up.
A 'tight' No3 elastic is pretty similar to a loose No4 elastic, and so on.
However, they are no use on elastics through one section (not advised anyway) because they won't fit inside the top section of a pole.
Gareth Purnell, Improve Your Coarse Fishing

1.
It’s unusual to get the elastic tension exactly right first time. You want it to slide back to the connector gently, but all too often it will either snap back or hang out the end like this. The Tippex stripes on the pole tip are a quick reference for the pole elastic strength, in this case a Vespe No7.

2.
First thing to do if it’s hanging out and too loose is check that the elastic is running smoothly by adding some pole elastic lubricant (10 drops is enough) to the inside of the PTFE bush.

3.
It can also help if you spray or squeeze a little lubricant down the inside of your pole. Simply remove the bung and spray the lubricant inside the carbon section. Replace the bung securely and test the elastic again.

4.
Here are two great trouble shooting devices that help get the tension ‘just right’. The first is my favourite Vespe bung, with the winder at the top, and the second is called a tensioner.

5.
When I set up I make sure I have two or three turns of elastic on the winder part of the Vespe bung. Then if it’s too tight I can release a turn or two, and if it’s too loose I can wind more on.

6.
The tensioner sits inside the pole and does the same job of altering the tension. This can be really handy if you want to tighten up the elastic during the session if big fish move into your swim.