If you worked for 6 hours 48 minutes in total you should have had at-least 30 minutes of break and at-least 15 minutes of that break should have been taken before going over 6 hours working time, but you definitely won’t be fined by the DVSA for a WTD infringement so don’t worry about that.
As for you being sacked for getting 5 infringements, I’ve worked at companies where they have a policy that says if you get x amount of infringements in x number of months (usually about 3 or 4 in about 3 months) you have to do training or a driver assessment, being sacked for getting 5 infringements seems a bit extreme but I suppose there’s probably nothing to stop a company having such a policy, you need to find out exactly what the companies policy is.
Depending on the job most drivers will pick up the odd infringement once in a while, but try to comply with the regulations and you shouldn’t have any problems 