So as a Muslim if you don't pray properly, what happens?
There is a big difference between not praying (salaah) correctly and not praying the 5 daily prayers.
If someone does not know how to pray or makes a mistake then they are excused but must try their utmost to learn and correct it.
Whereas, deliberately not praying the 5 obligatory prayers takes one out of the fold of Islam according to the scholars based on the following.
The authentic says of the Prophet (peace and blessings of Allaah be upon him): “The difference between us and them is salaah. Whoever neglects it is a kaafir (have disbelieved) .” (Reported by Imaam Ahmad and the authors of Sunan with a saheeh isnaad); and: “(Nothing stands) between a man and kufr (disbelief) and shirk (associating partners), except prayer: (whoever neglects it becomes a kaafir (have disbelieved) and a mushrik (polytheists).” (Reported by Imaam Muslim in his Saheeh, with other similar ahaadeeth).
And the Qur'an says about prostrating (praying):-
7:206 Surely those who are with your Lord are not too proud to serve Him, and they glorify Him and prostrate themselves before Him.
17:109 And they fall down on their faces, weeping, and it adds to their humility.
19:58 These are they on whom Allah bestowed favours, from among the prophets, of the seed of Adam, and of those whom We carried with Noah, and of the seed of Abraham and Israel, and of those whom We guided and chose. When the messages of the Beneficent were recited to them, they fell down in submission, weeping.
22:77 O you who believe, bow down and prostrate yourselves and serve your Lord, and do good that you may succeed.
32:15 Only they believe in Our messages who, when they are reminded of them, fall down prostrate and celebrate the praise of their Lord, and they are not proud.
38:24 He said: Surely he has wronged you in demanding your ewe (to add) to his own ewes. And surely many partners wrong one another save those who believe and do good, and very few are they! And David knew that We had tried him, so he asked his Lord for protection, and he fell down bowing and turned (to God).
41:38 But if they are proud, yet those with your Lord glorify Him night and day, and they tire not.
53:62 So bow down in prostration before Allah and serve (Him).
84:21 And, when the Quran is recited to them, they adore (Him) not?.
96:19 Nay! Obey him not, but prostrate thyself, and draw nigh (to Allah).
So as you can see its a commandment of God to bow down prostrate to Him alone as an act of worship, not according to how we want pray to Him but, according to God's wishes.
The Messenger has believed in what was revealed to him from his Lord, and [so have] the believers. All of them have believed in Allah and His angels and His books and His messengers, [saying], "We make no distinction between any of His messengers." And they say, "We hear and we obey. [We seek] Your forgiveness, our Lord, and to You is the [final] destination." 2:285