Can you contest a will if property is tenants in common?

Can I as a tenant in common contest my late husbands will? I signed a transfer of property form stating that we were joint owners but it was never explained to me at any point that I was signing a 'tenants in common' agreement. I have lived in the property with my husband for 19 years and have invested thousands of pounds of my money on renovations. Now it transpires that I actually only own 40% of the property in a tenants in common agreement.