Take a progression and peaking approach. Cut out the fast stuff for a few weeks, while you build extra mileage in at easy and steady paces. Then reapply tempo and reps when you're sure you're able to deal with the extra mileage load.
or stay as you are, and just add an extra 4-6mile easy run or two over the next few weeks.
I think either approach will get you there. Run it through your coach.
Am presuming you're a young lad, and that track sesh is with a club? Any coach there who can guide things along? That's the ideal long term solution for greater gains than this mere benchmark of sub 17.
Otherwise, in the short term, I'd experiment with adding an easy run, and not doing that parkrun every week. You're basically trying to do 3 hard sessions every week which without knowing the full details sounds a bit hefty.
Similarly, I wonder if that parkrun you do is even that fast a course!? You might find there's one local that is faster, and thus gives you a super easy route straight away.
My local parkrun for example has steps, inclines and grass. I could never go sub 17 there, but have done elsewhere.