I know it sucks but you haven't done anything wrong to get GD.
Your job right now in the early stages is to monitor your diet and monitor your sugars. Keep a record of everything you eat and the results of your tests.
You may not be able to control your GD with diet, that doesn't mean you've gone wrong it just means your body needs medication to sort this out.
If I remember correctly (been 8 yrs) the days where I started with a high result it was hard to get on top of and it stayed high all day.
So go back to the earlier advice.
Stop eating at 7pm today, if you need food in the evening make it protein/fat.
For the rest of the day be careful of your carb intake, stick to low GI foods and plenty of protein/fat. For main meals I would replace the pasta/rice/potato with green beans/mushrooms/asparagus/broccoli. Really really good roasted with olive oil and garlic or pan fried with a big knob of real butter.
Take a walk after your next meal, just 20 minutes walking can help your body to break down the sugar and bring down your levels. If you don't fancy going out then try a Lesley Sansone walking exercise video on YouTube. If you have young kids invite them to join in and have a bit of fun, if you have older kids or a partner who are full of sass then maybe wait till they're not watching 😂
Tomorrow, nip to the shop and stock up on things like babybel/cheesestring, nuts, green veg, eggs (boil up half a dozen and keep in the fridge for snacking and quick lunch options), cooked chicken legs/wings.