Yep, I agree. From your photos, it looks like you cut the motor drive chain too short.
Normally, you should be able to do the following:
Before you install the motor drive chain, adjust the bicycle chain so that it’s properly adjusted. The axle for the back wheel should not be all the way back in the slots, there should still be some adjustment left. If it’s all the way back, you would remove a link or two from the bike chain with a chain break.
Once the bike chain is adjusted properly, you would put the motor drive chain on and it should be long enough to be just a little loose. If you can’t put the chain on, you cut it too short and you’ll have to add in some links. The motor drive chain should be long enough that you can use the chain tensioner that came with the motor kit to adjust it properly. If you do it right, you can position the chain tensioner fore and aft and up and down to get the motor drive chain tensioned properly without moving the wheel (so the bike chain remains properly adjusted). See attached photo of motor drive chain on my bike.