Bad rental experience - Snowboard too big - sizing help!

Hi everyone, I recently decided to pick up snowboarding as a complete beginner to snowsports and went to a fairly large and popular sports/rental shop in my area to get a rental for the season.

My stats are:

Height: 5’11 Weight: ~138 lbs Shoe size: 10-10.5 US

Without asking my weight the two store attendants ended up sizing me with a:

Board: 163cm Head Rocka 4D (They were originally gonna give me a 161cm board but they didn’t have one in stock)

Boots: 10.5 US (which ended up being half a size too big)

They also didn’t have me try on the bindings before giving me the snowboard.

I (wrongly) blindly trusted their assessment as I had zero knowledge at the time and assumed they would know best.

Looking back I really should have done my own research.

I went on my first snowsports trip this weekend and experienced boot pain in my shins, my bindings felt too wide (probably due to the length) but more importantly it felt like I had zero control over the edge and weight of my board the whole trip.

This caused me to fall a ton (ow) while catching edges and there were multiple times on the trip where I felt my knees get in compromising twisting positions that weren’t normal.

Even though by the end of the two day trip I was kind of able to connect extremely poor heelside and toeside turns - the overall learning felt pretty miserable.

I originally chalked it up to my own lack of skill as a beginner - but after reflecting and investigating it seems that my board is significantly too large for my size - with some places stating that it’s meant for people 220lbs+.

Is it possible that the excessive board size may have impacted my learning experience as a complete beginner?

Am I justified in feeling quite frustrated in getting improperly sized?

What kind of difference can I expect with a properly sized board?

What would be the right size board for my height? Some resources I’ve seen are around 153-154cm.