Are you able to borrow at TT helmet? It would be worth it.
Also can you buy some slipstream bootie covers for your shoes- also well worth it.
And maybe borrow (and test ride a few times) clip-on aero bars as well. However for your first time the aero bars are not a must.

However from articles I have read a TT helmet and shoe botties DO make a difference as well as wearing your tightest cycling clothing (no flapping jackets or vests).