General aviation pilot reported a near miss when they misunderstood ATC instructions in the traffic pattern and turned in front of another aircraft. ATC then issued a traffic alert and provided separation instructions; the pilot complied with the ATC instructions and landed safely.

Narrative

On this day; I was taking my checkride. I was on downwind after preforming all other Airmen Certification Standards (ACS) required activities to satisfaction. Because of my lack of calmness; I may have misunderstood ATC directions to continue downwind and remain in the sequence. I continued on downwind and by the time I had got parallel to numbers on the runway; I was advised to adjust my speed by the DPE beside me since it was not good enough for a traffic approach.I looked to the right; checking for traffic; and took note an aircraft short and final. I passed a little bit; looked to the left for a while to look for other traffic on final and did not see anyone. As a result; thinking I was next in the sequence; I turned right and descended further into base. As a result; I put myself in front of another aircraft; causing the comms to blurt out; 'Traffic Alert.' The tower said; 'Aircraft X; make an immediate right turn onto final.'I complied and responded; and kept decent but not far enough separation from traffic behind me since I made a premature turn. The aircraft in front taxied away by the time I was 100 feet on short and final. Traffic behind me was at around 300-500 feet behind me but I am not fully sure. When I landed and stopped past the runway onto the taxiway; the traffic behind me came in on short and final. I taxied away and around that exact time the traffic behind me landed. As a result of the event; no one was hurt; no aircraft was damaged; and all was safe. However; although the tower or involved traffic did not say anything to me; my DPE said what I did was not safe and he would have to fail me on my checkride. I agreed and was just surprised I had made such a silly yet vital mistake. There was no direct and negative consequence; but I knew that if I had made that turn just a few moments later; I sure would have caused a terrible mid-air. I have reflected on that event and used that knowledge on the practice flight right after; and the checkride redo that next day; to ensure that I wasn't intimidated by the tower to just simply ask about directions if I was unsure about something. In-fact; I flew right after the checkride with my instructor just practicing ATC communications; and I asked tower if I needed to extend my downwind; to which he replied yes- just like the traffic scenario I was in just earlier that day. Except both people on final this time were jets. I was not going to make that error ever again and I hope that I never will. I redid my checkride today to prove to the DPE that I learned my lesson and that I was safe in towered airspace; which was routine for me but I had made a nervous mistake because it was a checkride. Regardless; the point remains on the recklessness of the turn.What I did was unsafe; and I have reflected on that to ensure I can start my journey as a private pilot safely.