A proposal opens a decision rather than announcing its result. Try, "Would you like to visit the exhibition this weekend?" If your friend says, "That sounds interesting," you know they may be interested, but you have not yet agreed a day or bought tickets.
Ask a useful next question: "Would Saturday morning or Sunday afternoon be easier?" Offer choices you can actually manage and leave room for another suggestion.
Check the detail that affects commitment
In a practice exchange, your friend might ask, "How much are the tickets?" Reply accurately: "I have not checked yet. Let us look before we decide." Do not invent a price to keep the conversation flowing or assume your companion accepts an unknown cost.
Once the details are settled, state the arrangement: "So, Sunday at two, meeting outside the main entrance. I will book our tickets after you confirm the price is okay." That final condition should remain visible until it is satisfied.
Practice another version in which the person declines or suggests a different activity. Respond to their preference instead of forcing the original proposal through a memorized script. A successful planning conversation can end with an agreed alternative or a clear decision not to proceed. The language should make each person's choice and the current status of the plan understandable.