Learning to fly is a process. No one gets it 100% right in the beginning. It is said that at the same time you get your PPL, you get two buckets: one empty, one full. The empty bucket is your (lack of) Flying Experience, the full bucket is Luck. The trick is to fill the bucket of Experience before the bucket of Luck runs out!
Your Instructor will have trained you to fly within certain safe parameters. These are your building blocks. From here, you now have a license to learn. Stick to the guidelines, and you will live long enough to become an old, experienced pilot.
Your Integrity Along the way, as you are learning to fly, you may do something you realised afterward was perhaps not too clever. It is very important to own up if you have done something that could cause someone else harm down the line. No one wants to look bad, but choose the path of self respect and integrity and own up if you have. It is not the 'easy' route, but it is the right route.
Mistakes that Cost I have made some mistakes I am not proud of... I have even made mistakes when flying :P You will hear about some of these errors in judgement "anonymously" in the links below. I have never stopped learning to fly. There is always a new lesson to be absorbed.
Some things I have heard about where people didn't own up was a nose wheel landing, resulting in the next guy taxiing out and having the nose gear collapse on him, causing a prop strike. It would have been a lot cheaper if the nose striker had said something.
I have heard of an aircraft wing becoming separated from the aircraft body aloft resulting in two fatalities. The investigation showed it was due to airframe stress... apparently someone went through Vne and said nothing.
Do the Right Thing So do what is right. Own up if the flight didn't go so well. You may be saving huge costs on the aircraft, or even the next pilots life. What if that next pilot is you?
About Landings: You may have heard that the definition of a 'Good Landing' is one that you can walk away from. The definition of a 'Great Landing' is one after which you can use the aeroplane again.
May ALL your landings be GREAT ones!