Spread ur meals across if you can.
You want mass or strength? Plan your workout

means eat more smaller meals than 3 huge portion of meals a day.
your training seems rather light to me even for a first timer.

as mentioned your workout is rather light to me.

Sat:
Arm Extension
17.5kg X 15 Reps
17.5kg X 15 Reps
17.5kg X 15 Reps

Chest Press
20kg X 15 Reps
20kg X 15 Reps
20kg X 15 Reps

Mon
Monday
Shoulder Press
15kg X 15 Reps
15kg X 15 Reps
15kg X 15 Reps

So sat is ur chest+arms day, from there, i can see that u are doing split workout. 3 sets per muscle group per workout and once a week? that's a bit too little....

are you worn out after your workout?

..as expected, your workout is too light ...you either have to increase the weights or increase the sets, else you are just wasting your time hitting to the gym. nonetheless, if you just want to sweat then you might be doing the right thing.