Small Aircraft
Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 7.6; Flight Crew Total 848; Flight Crew Type 65.5
Human-Machine Interface; Confusion; Situational Awareness
Conflict NMAC
Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Procedure; Human Factors
I was coming from the North and was entering the right downwind.  I was given an extended downwind by the Tower Controller and a 'number 3 clear to land'. I had switched to my ADS-B traffic page on my GTN 750 navigator; which I always do to improve traffic identification in the traffic pattern.  Tower Controller mentioned that number 2 is over a VFR reporting point.  I saw the traffic over that point at my 1 o'clock position.  In hindsight; I am not so sure anymore whether this was actually number 2.  The 1 o'clock angle looked right to me and I saw the traffic; a high wing; and pointed it out to my copilot. It was about where the reporting point is located (at least that's what I thought).  I did not verify with my ADS-B traffic page; which would have clearly shown the number 1 and number 2 traffic.I was focused to look outside for the traffic.  I let the traffic pass on my right and continued a little bit further downwind; since my plane tends to be faster; so to give it more separation. Then I turned base; then final.  I was slightly high so extended full flaps. The gear was already down.  All of a sudden on short final; I saw 50 feet left; 200 feet ahead and 100 feet below of me at about 11:30 o'clock position a high wing plane. I immediately turned right and did a 360; and let the Tower Controller know.  Rest of [flight was] uneventful. I am still a little bit unclear about the exact positions of number 1 and number 2 traffic. I was number 3. The most likely case was that I mistook number 1 as number 2; and thought number 1 was on short final. So I did not pay attention to number 1 but only looked for number 2. If I would have paid attention to number 1; I would have recognized that there is no number 1 on short final; and that the plane that I thought is number 2 is actually number 1.Further; I did not cross check with my ADS-B display. This is exactly the kind of situation; where ADS-B helps greatly and in the most important moment I did not cross check; a clear mistake. In summary: When number 3 or number 4 and cleared to land; make sure all ahead are accounted for. Identify number 1; 2; and 3; so to not mistake number 2 for number 1; or number 2 for number 3.  Usually; I do that; but in this case; I was sure; I had identified the position of number 2 correctly. Cross-check with ADS-B traffic page. Contributing factor was that the audio traffic alert from the GTX-345 transponder to my headset does not appear to work. This may have been due to a recent avionics upgrade and I have to fix.
GA pilot reported they misidentified the traffic in the RNT airport pattern after being instructed to follow and turned onto final too soon resulting in a NMAC with preceding traffic.