Distance out is a factor
Many new fliers start out flying in on top of themselves. My suggestion is depending on how far out you are to maybe fly a little further out...This will help in determining you altitude.....
I have not seen you fly and only based on what beginners try to do at first am I making this recommendation. Usually a new guy will be flying just off the far side of the runway. You need to be out at about 150 meters of about 500ft away......
Now smaller planes like 40 sized stuff will be too small out this far.....by try it.....
Consistent altitude and heading are the tools that you learn in Sportsman-Intermediate and Advance......So if you are flying Sportsman you are in the right class to learn these...as you progress up through he classes these same criteria are your nemesis when doing more complex maneuvers.
Its tough but you are not alone and it doesn;t make you a bad flier....just gives you that goal......So take the deficiency and work on...It takes lots of time to perfect.....Even today I have been flying pattern since 1987 I struggle sometimes with proper altitudes and headings....My problem is out west we can fly really low. When you get back east there are things called trees and they can eat airplanes....
So try to move it out a bit and keep plugging away.....
Where are you because it would help if you had a helper? Maybe we can wrangle up an experienced pattern flyer to help you out.....This works wonders on the flying and your confidence too.
Troy Newman