Newbie first timer, looking for understanding

Hi thetagang! Just want to clarify something. I’m using SPY as an example. I’m looking at selling cash covered puts for Sept 18, strike 772. As of right now it’s $11.35 per contract. So if I sell this put I’ll collect $1135, but if I want to be safe I need to hold onto $77,200 until Sept 18 to make this $1135? I see screen shots here where ppl have 100s of trades, how do they hold onto their money that long for that many trades? And $1135 is only 1.5% of the $77,200 that I need to hold onto for a couple weeks, seems like I’m missing something here. Thank you for any comments / sage words in advance!