That bike is too small for you..

I'm 5' 11" tall and my old road bike was a 24.

You also most likely need stronger upper chest muscles.
Those take some training to hit.
for instance,
On your back on the floor, 10 lbs to start in each hand, move up as needed,, 20 to 25 should be your sweet spot.
elbows on the ground, just below level with the shoulders,
say elbows about nipple height,
forearms straight up, 12 o'clock,,,,,,,,,,,

Here is the biggie to hit the upper most chest :
When you bring the weights together they should touch above your belly button or belt line...

NO point of failure reps ever ! start with a dirty dozen,, max at 14 reps,,add weight as needed.

Your neck hurts because it is not supported from the front, leaving the back neck muscles, these are tiny, and upper shoulders
to hold your 14 pound bowling ball of a head up.....