FWIW I've been wrestling with similar issues. Was getting good #s on people initiating checkout out on my landing pages, but no follow-through. I recently hired this guy on Upwork for an audit, which was super insightful. Link if helpful:
https://www.upwork.com/freelancers/~01aeafccdd092cdaad (I think you need to be logged in to view his profile)
Where are you running your ads? And what's your goal with the Google Form (e.g. lead-gen or purchase?)?
Personally (aside from a lot of landing page design blunders), I learned I was not thinking about funnels properly. The offer needs to match the pay-per-click channel temperature. For me at least, it's not as simple as a single funnel with Ad->Landing Page->Sale/Lead -- getting cold traffic to convert is unlikely.
For me, I need to build something more like (super roughly):
1. Top of Funnel campaigns (w/ cold traffic): Ads with a goal of building up an initial/top audience from cold. Mainly looking for engagement to build awareness. This might be giveaways of some sort.
2. Middle of Funnel campaigns: using audience from top-of-funnel & mainly looking at website/product viewers, have an offer that results more in lead capture: free trials / etc.
3. Botton of funnel campaigns: retargeting leads, people who initiated checkout/abandoned cart. etc. -> more aggressive offers like a bigger free trial