Please put a pillow beneath your wife's back and stand in front of her have a dim light and use a water based lubricant like KY jelly or any ultra sound gel to be applied on your erect penis and insert it in the same place where your inserting your fingers. This position will not put weight on yr wife and you will be able to see better and with her pelvis supported by pillows it will be easy for you to insert. If you are still unable to do it kindly consult a good certified competent experienced clinical sexologist even if it is online via practo or cupidcare or lybrat e.com
Next Steps
Relax and buy some lubricants and use the position as described above
Health Tips
If you are uncomfortable please consult a good sexologist at the earliest even if it is online