I had a big gap from driving trucks from about 1995 until 2005 ish and so went straight from 10 years of not driving a truck at all and being given a truck with digi tacho! I made a complete dogs breakfast of it!
I can remember taking my break on dinner time one particular day and I’d sat there a good 20 minutes before I realised I’d not actually put it on break!
Another balls up saw me take a 15 and then I wondered why my red driving time message was flashing up on the dash after 4.30 drive time. 
You’l also leave your card in all night on other work sooner or later!
We all gota start somewhere. As Harry said above, dont beat yourself about it, DVSA are looking for the real ■■■■ takers, not drivers who make a genuine mistake and new to the job!
These days I occasionally get a crapagram from the analysis company if I go over my WTD break by 2 minutes, I ■■■■ you not!