You need to talk to your tutor if you feel that you have not had experience of anything you're expecting to come up in the exam.
As far as forgetting what you have done, you should be able to use your portfolio to revise. Try the following method, many people find it is remarkably effective but it does take some effort and concentration:
Work through the portfolio, one case at a time. FInd somewhere quiet where you won't be distracted and turn off your phone. Start by just looking at just the title of the first case and then try to remember as much about the job as you can, starting with your arrival at the site. Try to recall as much detail as possible, including smells, sounds, etc. Then in your mind go through every step of the job remembering as much detail as you can, remember WHAT you did and WHY you did it. Have a short break, e.g. for a cup of tea, then repeat the process but this time look at the photos and descriptions in your portfolio in sequence as you go along. Now give it a rest and repeat a final time the next day after a night's sleep. Then move on the the next case.
You can do more than one case at a time but don't try to do the whole lot at once as if you do this properly it'll take time and be surprisingly tiring. The key thing is to RECALL each case IN DETAIL at least THREE TIMES with a break for SLEEP between the second and third times.