If you passed the uncoupling / coupling the first time, it is understandable that this wasn’t made a priority in the limited time you probably had for practice.
For the next time, obviously know where the catch is.
If you are worried about the king pin not engaging:
- Make sure the release handle is out (it should be).
- Make sure the fifth wheel is in contact with the trailer and near enough horizontal. Get out and raise the suspension a couple of inches to make sure, even so the legs are off the ground
- If you have done the above and you are in alignment, then don’t be afraid to give it some welly. The fifth wheel has a V like cut out so any slight miss-aim will be corrected. If you have raised the suspension so the landing legs are off the ground (or at least most of the weight is off them), these are not going to be damaged by coming back with some force and even being slightly out of line.
If by some weird chance you cannot get the clip in, you may have a partial engagement. If you are tentative with coming back this may be more likely to happen. In this case, pull the release handle out, draw forward and come back again.
The tug tests are also a must I believe, so don’t leave these out.