I think I bought the wrong bike
First thing is ( as suggested by @whatsisname )go back to the shop and ask for an exchange, explaining why. Worst happens is they say no.  

Presuming they say no, have a conversation about about finding a way to get you onto a bike that suits better.  You will essentially have have two choices - try to make the bike suit you better, which will almost certainly have limited success, or write it down to experience, sell the bike for what you can get for it and buy something more suitable. Keeping in mind the total cost of the bike, I do not recommend spending money making it fit better - it will only ever be a comfort bike. 

Free stuff - things like seat height and handle bar height. If the bike shop that sold it to you will not take it back, they should make some adjustments for you (If not, put the cost down to experience and find a better bike bike shop).

Looking at the picture of the bike a few thoughts-  the rear spring/shock will be gobbling up power as you pedal. Tighten the preload as much as you can (or replace the 'shock' with a solid tube).  The effective top tube length (The tube that goes from the seat to handle bars) appears very short. This gives a very upright riding position which is less than ideal for speed (but good for comfort). Not much can be done to change this - putting the seat back as far as it will go, and lowering the handle bars might help a little. 

Pump up the tires to a reasonable pressure. Check sidewall for max pressure. Play with pressure starting at highest on side wall and lowing it a few PSI at a time till you find a sweat spot of comfort vs rolling resistance.