Debating installing a replacement liner

So, I'm battling with myself on this. I have a 15ft AG pool with the original 12yr old liner that is about to be replaced along with a brand new skimmer and return.

I've seen countless youtube videos on installing the liner and it does not seem that daunting. My fear is that somehow I will mess something up or an unexpected problem will arise that I cannot handle (ripping the liner, etc)

So what's killing is is that pool installers in my area (Northern NJ) want between $400 - $450 to install my new liner ( I purchased it online for $180 and the skimmer was $40). That install price includes tax and any sand needed. No wall foam or floor foam has been mentioned with any of the installers. My thoughts are that if I haven installer do the work, it's guaranteed until the end of the year. If I do it, I'm guaranteed nothing. I'm sure I'm not the only person who has felt this way. I know, well I hope I know, that the installer will do a much better job than me.

Thoughts? Am I over-thinking? Do I need wall foam or floor pad? ...

Thanks
Joe

Here's my thought: If you try it and screw it up, you either have to start over with the same liner (assuming you didn't trash it beyond use) or get a new liner. Odds are, the skimmer will still be fine.

So...say you screw up the line and need a new one. Odds are you won't make the same mistakes twice and it will work. That's $360 in liners, vs $400 for the install--plus the liner--$560. You could even have to put in a THIRD liner and still come out ahead!