If you had a packaged autosiphon and the tubing included, it is probably the right size. It is very difficult to get onto the end of the cane. I usually need to take a cup of water and heat it in the microwave. I then dip the end of the tubing in it for a while which softens and makes it more pliable, then I can get it on.
When you start a siphon there is sometimes a pocket of air at the junction of the cane and tubing. It sometimes looks like air is getting in but it is really just bubbles going down the tubing a bit then coming back to the junction over and over again.
If you did not have a tight joint and air was introduced, the beer is likely to be oxidized. I would bottle condition and try one at about 1 1/2 weeks. If it is well carbonated and tastes OK you might condition a bit longer. Check a bottle periodically and when you get good carbonation, chill all of them and drink them relatively quickly, if oxidized the wet cardboard taste will get worse given longer aging.