On medical ceritficates

Hi! I'm in need of help, I'm currently pregnant and employed. During my first trimester I was having a difficult time and was very depressed. I filed for a leave of absence and it was approved for one month. However, by the end of that month I was not ready to go back to work and asked for an extension since I had fever and was still feeling under the weather. I was absent but my manager tagged me as no call no show and told me that I have a return to work order already so he can't extend my leave. I asked for a medical certificate but the doctor only issued bed rest for 5 days, now, I am not proud of this, but I altered the said document and put 15 days instead.I had to go back to work and there was an administrative hearing and I was found out. Will this be ground for termination?
What would be the best thing for me to do now? I'm sorry if I sound clueless, I really am. I badly need your advice.

yes, that is grounds for termination.