Lost and confused

I have a 2007 camry with a 2.4. I recently replaced the head gasket and set the timing. It will mot start and it is turning over real slow, people keep telling me the timing is 180 off. I have watched videos and gone through the manuel and according to everything I have read and videoa I have watched the timing is right. At this point I am lost and confused, I need to know I missed a step

First, get the battery on a charger overnight. That’s probably the cause of your slow cranking. Second, check fuel pressure and spark while cranking. Lastly you very well may be 180° off. Check it again.

Find and chalk your timing marks. Remove spark plugs.

Have someone rotate engine with the starter. Air should be coming forcefully out of the #1hole if you are in time and out of the #4 if you are 180 off.