Rob,
As has been said earlier in this thread-you dont need a degree to become a pilot. If i may add some perspective to your situation-I wasn’t clever enough to get a place at uni to study aero eng. Instead I went and studied something easier. By getting a 3rd in your degree I’d suggest you’re more intelligent than me!
I’ve been in the RAF as a Pilot (and now instructor) circa 15 years now. Never needed my degree, although it may come in useful as a back up / If I lost my medical. Beyond initial application stage, I don’t think anyone cared about my degree.
I’ve also now got my CPL/IR, and the atpls are certainly not anything harder than A’level (if that). Just a huge volume to get through.
Concentrate on your degree-you’ve nearly finished it! And i would be amazed if getting a 3rd would in any way negatively impact upon a career as a pilot.
Good luck!