A few comments on your post. Manufacturers are allowed a 20% error in reporting calories so you might be way off and they never seem to err on the high side of calories, but the important fact is that if you are putting in mfp what you read on a label, you are eating the wrong food, unless it is a can of bean or packet of frozen berries. Eat whole food. A steamed cauliflower, a tomato salad with slices of read onion, ..
Can you go UPF and label free-ish for a week within your calorie allowance. Look at the labels, anything that has sugar in it, you ditch, anything that has a combo of letter and numbers, such as 415, 341, E, ...emulsifiers, preservatives, leave on shelf....
Deli meats, such as ham and sliced beef have plenty of stuff in it. I didn't mention the mackerel or say you shouldn't eat it, however too much salt will not help your weight loss. Have you tried poaching frozen cod? Cold in salads, it is delicious, low in calories and high in protein.
Your next shop, buy in the fruits and vegetables section, fresh meat and fish, even fresh dairy, skip the bakery section, and if shipping in the middle aisles, only stick to whole foods, such as brown/wild rice, steel cut oats, legumes, frozen spinach cubes, frozen prawns (nothing else in the packet) ... minimally processed.
The quality and source of your calories matter. The same ingredient processed in different way will be accessed in different way and your body will extract a different amount of calories from the same food. As an example, whole almonds : 579 calories per 100 gr. But the body will use a fair amount to break the cellular matrix, so in the end, you can cut 30% off those calories, just to break the almond down and make it accessible to the body. Almond flour, same calories, 100% available. No break down necessary. Two foods, same ingredient, same calories on packets, not the same calories accessed by your body.