movement: push, direction: up!

so we didnt run yesterday...only four of us showed up and the instructor wasnt feeling well, so we did a pseudo circuit class between the four of us.  lunge, pushups, squats, more arms, more tricep pushups...

i have to say that the pushup is my primary area of weakness.  i can do proper ones on my knees.  but from my toes?  f-that notion.  honestly.  i see the instructors do it and they're straight as boards.  me?  i'm sagging and doing "the worm".  brutal.  i've been in enough fitness classes that i should be gaining strength in my arms, chest, and core to pull that off, but it's not working!  i can probably do 1 or 2 proper ones and then i'm either doing a funky 80's move on the floor or rolling my eyes and lowering myself to my knees. 

i feel as if i'm cheating myself by not doing proper pushups.  frustrating!