just bought a 2007 prius help

im new to prius i bought a 2007 touring prius and i had to buy a new 12volt battery and i had to change the cooling flow valve because it showed the code for faulty cooling flow valve i changed that in the prosses it was parked with the hood cracked and doors unlocked some how i drained the 12 volt battery so i bought a new one. everything powers on the ready light is on and when i put it into reverse the backup cam comes on and beeps and i give it gas and it acts like the breaks are on i dont have my foot on the brake and i give it alot of gas and it will not move im parked on a mild slope and have been parked on this mile slope the hole time for the repair and order for the new battery the parking brake is not pushed and has not been on the whole time ether i dont have much room in front of me to roll forward but when i put it into drive it moved a little forward but when i put it in reverse it acts like its locked up everything was fine other than the code prior to the repair i just wanted to get the check engine light off so i could get it smogged for the title transfer im am clueless and i can not find anything online about the situation im having thank you for any replies robin

 

crazy thing is i went out again and all be dammed if this time i when i put it in reverse it kinda felt a little different and it reversed when i pressed the peddle.. now yes im a girl but im pretty good with working on cars my Pontiac grand prix has been had its problems and im not one of those girls who will sit their and wait for somebody to fix it for me i will get on you tube and websites and most of the time i do the repair myself new manifold , thermostat the water pumps every censer to do with the evap gas tank fixing codes for smog anyway . so when i put it in reverse it feel different . i dont know but it works now . im seeing the mpg fluctuate from 0 to 99.9 in a distance of one residential stop sign to the next stop sign thats a very wide range is their something electrical wrong

 

just to confirm so it is normal for the mpg to keep fluctuating rapidly up and down and never settling on any number but 99.9 in the time it takes just going from one stop sign on flat ground to the next at a speed of 30 mile a hour with my foot on the gas getting up to 30 mile and hour and before i take my foot off the gas before the next stop sign and it settles on 99.9 before i got to let off the gas peddle for the stop sign thats normal

 

know sooner i got the cooling valve changed the 12 volt battery went bad got a new one and then the code for the hybrid battery came up and the red ! on the dash and now while i was trying to figure out the hybrid battery situation somebody now has stole the converters i just dont know 1800 i payed for it 200 on the valve and 12 volt now this and im in california. i really just dont know im threw ..i have a few converters around here but all for different vehicles some oem some aftermarket .. oems from other vehicles if i weld them on will they throw a cat code i just dont know a low cost way to replace so i can pass smog anyway. im probably going to just have to give up on the car.
im sad