General aviation pilot reported improperly entering the pattern causing a near mid air collision.

Attributes
ACN	1515669
Time
Date	201801
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	Amateur/Home Built/Experimental
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Route In Use	Visual Approach
Flight Plan	None
Aircraft 2
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Flight Plan	None
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Private Flight Crew Instrument
Experience	Flight Crew Last 90 Days 1.0 Flight Crew Total 1100 Flight Crew Type 600
Events
Anomaly	Conflict NMAC Deviation - Procedural Landing Without Clearance
Miss Distance	Horizontal 200 Vertical 100

Narrative:

I called in to tower after switching from flight following to do some touch and goes.I was told to enter on left base for 30 right. I can't remember if I was cleared to land.no tower responses to anyone else were heard. Tower then changed my entry instructions to 'enter on full left pattern'. I was close to pattern already and traveling at 145 kts.I entered too far downwind; closer to abeam tower and at that time tower advised me a cessna 172 was in pattern and on downwind. I looked left and there he was so I dove down to avoid further hindrance to his flight path. And I flew an extended downwind at a higher rate of speed. And we both continued to work the pattern.I didn't know another plane was in the pattern; the long runway with a 5000 ft displaced threshold played perception tricks on my eyes. I entered improperly into pattern and it had been two months since flying.I need to practice more often and slow down and use 45 degree entry on the crosswind to downwind area to enter pattern.

Original NASA ASRS Text

Title: General aviation pilot reported improperly entering the pattern causing a near mid air collision.

Narrative: I called in to Tower after switching from flight following to do some touch and goes.I was told to enter on left base for 30 right. I can't remember if I was cleared to land.No tower responses to anyone else were heard. Tower then changed my entry instructions to 'enter on full left pattern'. I was close to pattern already and traveling at 145 kts.I entered too far downwind; closer to abeam tower and at that time Tower advised me a Cessna 172 was in pattern and on downwind. I looked left and there he was so I dove down to avoid further hindrance to his flight path. And I flew an extended downwind at a higher rate of speed. And we both continued to work the pattern.I didn't know another plane was in the pattern; the long runway with a 5000 ft displaced threshold played perception tricks on my eyes. I entered improperly into pattern and it had been two months since flying.I need to practice more often and slow down and use 45 degree entry on the crosswind to downwind area to enter pattern.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.