They don't care.
I have travelled so many times in these past two years. T&T called me once out of the 9 times I travelled, and only on day 4. They asked if I had taken the day 2 test, I said I hadn't because I never received it.
I didn't get the test kit until day 7. By that time, I didn't bother because I had no symptoms, and I had already done a lateral flow and I just wanted a refund from them.
Point is, when they asked me if I had done they 2 test and I explained how annoyed I was it hadn't arrived, they said "oh well, sorry it's not our fault, no lab is Gov approved, so you will have to take it up with them. Hopefully they arrive, if not, then try to get a refund" then I never heard from them again.
They didn't care the I wasn't able to test and didn't recommend an alternative. They didn't check any further to see if I was isolating. To say I was furious is an understatement. It is all a money grabbing scam and the government are at the helm of it.
My uncle once had someone come to his door to check he was isolating on day 9. He broke isolation to go to the shop, and his daughter answered the door. They asked where he was, she told them he popped out to the shop, and they said, ok. That's it. All the checks are at random, they do not have the resources to really enforce anything.
Of course you must be nervous now because you don't want to break your isolation, but you aren't a risk to anyone, so just carry on with your life. If they call you, pretend you're at home, they aren't tracing your location.