MR - I certainly wouldn't concern myself with the "chop rate" at college at this stage if I were you.
The chop rate varies enormously from course to course - there is no "chop quota" that the college has to meet to prove to SRG that its courses are feisty.
On my course of 29 students, 28 graduated and are still gainfully employed. ALL 29 are still employed in ATC in some capacity. The course before was decimated, so the overall chop rate may well be 30%, but it's not something to lose sleep over. You've done the difficult bit by getting on to a course. If you keep your head down, college will be plain sailing.
Incidentally as Bright-ling said, the college is supposed to be moving to a system whereby students are chosen for a rating on day 1 and don't waste time failing aerodrome courses when they're destined for area control. This should reduce the number of needless casualties and also get people through the system quicker. However, given the pace of change in the company, I suppose it might be installed by 150 course!