First, if I understand the question correctly, hit the End key the CTI (aka timeline cursor) goes to the end of the comp. Hit the e (for end) key to extend the comp workspace. AE will RAM Preview as much of the timeline as there is RAM available.
Ah, but we don't know how much RAM you have! So you need to go here to learn the diagnositc info we need:
And third, YouTube tutorials can be iffy. It's far better to lean AE from the AE Pros instead of some high school kid who can miss things, don't you think? In which case, you go here:
oh boy, that's a list and a half!! Ok here we go
after effects cc 126.96.36.199 trial version for now and it shows up to date with a green check mark
windows 7 64-bit OS with auto update turned on
16GB of RAM
AMD Phenom II Quad core 3.30 GHz B60 processor
xfx R7850 Radeon w/1GB of video ram
video driver version 14.501.1003.0
Source footage is a .PSD file I created in photoshop which I can upload if you guys like
I do not run quick time
Software being used - photoshop, after effects, firefox, creative cloud application, avast anti virus
No third party effects, no openGL, no third party codecs, just strictly after effects
did not attempt to render, no ray-traced
Well I started a complete new comp and initially began with 450 frames and THEN I imported my photo into the composition and it's working fine now guys, apparently it kept using a default of only 1 frame when just dropping my image into AE the way it shows in the video.