dcstudios24 The attached screen seems perfect, only the "X" is missing, to close the form on the top right and at first glance I seem to notice that the buttons: send and cancel, have different size, should be the same.
To add image instead, You may try and override the default form from Joomla Core as per method outlined and then, make changes accordingly in the override file
The buttons size vary due to number of characters as "cancel" has more words than "send" and it is quite normal for background to resize based upon characters
I do not know why all the fields are small and not responsive ...
Kindly check now. Have added this to similar file where you can change width value accordingly for responsive mode :
@media only screen and (max-device-width: 580px){#mailto-window input{width:90% !important;}}