What type of BTEC are you studying? Certificate? Extended Certificate? Foundation Diploma? Diploma? Extended Diploma?
What subject are you studying? Business? Information Technology? Applied Science? Travel and Tourism? Something else?
(I ask as it's much easier to assess the impact of an individual unit on the overall grade if we know the BTEC type and subject.)
In answer to your final question, about resitting a unit, the BTEC rules say, with regards to BTEC Nationals, that "If learners resit an externally assessed unit, the best grade achieved will count towards their overall qualification grade, not necessarily the most recent sitting." This would apply to your unit 1, as that is externally assessed. You could therefore potentially improve your overall grade (and the associated UCAS points) via a resit of this unit.