So this is clearly a beginners project.
Probably the first ever PCB design you made.
Some good things:
I can open and view the schematic and PCB.
When I run a DRC check on the PCB, it even reports no errors, which shows me that you also probably also did the DRC check during the design process.
“There is plenty room for improvement” 
Now the “bad” things:
An electronics schematic is much more then a means to generate a netlist to make a PCB from. Those are not even the most important goals of the schematic.
The first and very important goal of a schematic is to make it human readable. This is so you (and others) can understand what is the meaning, and how it is supposed to work.
For example, It was only after searching on the 'net for the MAX756 that I found out it was a voltage regulator chip.
Another (obvious to me) thing that is missing, is a connector to put power into your board (This is normally a schematic symbol, just like IC’s and passive components).
The circuit for the LM35 is also not going to work. AVcc of the Atmega328 is a power input and should always be connected to the Vcc pin of the Atmega328.
There are also no decoupling capacitors on the board.
I also see 2 big caps: C2 which is 150uF and C3 which is 100uF.
Capacitors of these sizes are usually electrolitycs, but you use schematic symbols for non polarised capacitors. C3 is also a very small SMD capacitor on the PCB. That is never going to work.
There are also many other issues, and the amount of effort I am willing to put into this is limited. About a year ago I did this for another beginner. My advise to you is to read that thread and implement the advise given there: