@rainraingoaway86 the bottom line is your employer is acting unlawfully. However, being pregnant makes you extremely vulnerable.
The better option would have been for your employer to employ you via an Agency.
It is likely when you claim Maternity Allowance this will all come out.
To answer your original question, as you should be an employee you should have the right to return to your job.
You are going to have to talk to your employer about this but timing may be crucial.
A key date is 15 weeks before your due date. You must give your employer notice that you are pregnant (MatB1) and when you plan to take leave and SMP before this week.
I am going to suggest you talk to both ACAS https://www.acas.org.uk/checking-your-employment-rights/if-you-believe-your-employment-status-should-be-different and Pregnant then Screwed https://pregnantthenscrewed.com/advice-services/
Once you have done that make an appointment with your employer in the 16th week before your due date, do not let them defer this. Explain the situation and what they can do to rectify it (ACAS).
At the meeting give them a letter explaining you believe you are an employee and that you are pregnant and wish to take Mat leave from x to y dates including SMP. If they are not going to pay SMP please can they give you an SMP1. Make sure you keep a copy of the letter.
Point out that they can get 103% of SMP back from the gmt https://www.gov.uk/recover-statutory-payments it may help to ease the discussions.
Be prepared for them to not be happy as it will cost ££, also be prepared that they may terminate your contract with immediate effect. If they do try to get it in writing - don’t leave without it and go straight to the JobCentre to apply for Maternity Allowance and other benefits.
You also need to contact HMRC as your self employment is a fudge that needs resolving.