Hi
@Bmbz and welcome to the forum. There is a lot to get your head round with a new T2 diagnosis and one of the first things to understand is the idea of cutting out carbs altogether is not only unnecessary but is to all intents and purposes unachievable! Just about everything you eat contains some carbohydrate, some things not very much and some quite a lot and as Kaylz says, you are far better thinking about controlling the amount of carbohydrate you eat.
Having got that sorted, the second thing to understand is that there are no magic rules which, if followed, will make all things well again. The reality is that there are general principles but how you use those principles depends very much on you and how your body works. Read around the forum and you will find that the general principle of reducing carb intake is used by most, but there is a right old mixture of ways we have gone about it. Some go to very low carb with a wholesale change in diet. Others have done a bit of tweaking - removing a few things maybe and adjusting portion sizes on other things - simply to reduce carb intake to levels that their system can cope with. You need to find out what will suit you.
I think a good starting point is to understand how far up the diabetes ladder you are. You will have been diagnosed from the results of blood tests measuring your HbA1c level. Do you know what those results were? If you don't then ring up your GP surgery and ask for them for the numbers. If you are just over the diagnosis level then a few tweaks might do but if you are along way over than something a bit more drastic might be in order.
To come back to your question about the sandwich......
If you make them yourself, then think about the bread. Look on the packaging and see how much carbohydrate is in it. Look at other breads and you will see that there can be quite a variation in carb level. If your bread is in the higher carb bracket, then try something with less carbs. If you buy a sandwich then start looking at the packaging and seek out the lower carb options.
Above all, ask questions here on the forum and we will do our best to help you find a way through the maze. We all get it because we have all been where you are now. Most of us have found a way out and are more than happy to help you find your solution.