I too found the tablet kits hard to use, I had one way back in the 1990s and it took so long for the tablet to dissolve that I didn't know when i was supposed to start the clock for the timing
If the tablet kits are the same as liquid reagent ones, lighting can affect the colour in the test tube. Daylight is the best for reading the test, and old fashioned incandescent bulbs if you still have any. Fluorescent and compact fluorescent (energy saving) can distort the colour in the tube. Halogen bulbs are usually fine, though I don't know about LED bulbs.
It looks as though you did have some ammonia left behind. The thing to do now is add some more, enough to get the reading to 3.0ppm. It will be a bit of a fiddle but add it a bit at a time and wait 30 mins before testing to allow it to mix in. With the amount of ammonia you will need to add it may well be worth spending a £ or two on a 1ml babies medicine dosing syringe (from a pharmacy, the babies medicine bit is very important as you could get the third degree if you ask for just a syringe!). I have a couple of these syringes, they are graduated in hundredths of a ml and are very useful for small tanks for dosing everything from ammonia to medication.
Try adding 0.4ml ammonia and see what reading that gives, then add a bit more if necessary. Add up the total amount you add, that will be the volume of ammonia needed for 2.6ppm (since there is already 0.4 in there). Then you'll be able to work out how much would be needed for 3ppm and 1ppm as you'll need to add those amounts later in the cycle.
If you test your tap water as well as the tank, you will get a base line for the tank readings. Leave a glass of water to stand for 24 hours then test the pH - you will probably find it is different from freshly run tap water. It may also be different from the tank pH as adding ammonia does mess with the pH reading.
Your tap water may well contain some nitrate - the UK allows up to 50ppm. That way you'll know how much nitrate came from the tap and how much is made by the bacteria.
It is possible that the plants had some bacteria on them, a lot of people reckon that is a part of speeding up the cycle with plants. The plants may also use some ammonia as food, they prefer it to nitrate. If they do use a fair bit of the ammonia you add you won't see quite as high a nitrite reading as if you didn't have any plants. But the end result is the same whether the plants help or not - the cycle is finished when there is no ammonia or nitrite in the water 24 hours after adding a 3ppm dose (at steps 10 to 12 of the method in that link)